[PATCH net-next v1 00/11] xdp: page_pool fixes and in-flight accounting

[PATCH net-next v1 00/11] xdp: page_pool fixes and in-flight accounting

[Jesper Dangaard Brouer]

This patchset fix page_pool API and users, such that drivers can use it for
DMA-mapping. A number of places exist, where the DMA-mapping would not get
released/unmapped, all these are fixed. This occurs e.g. when an xdp_frame
gets converted to an SKB. As network stack doesn't have any callback for XDP
memory models.

The patchset also address a shutdown race-condition. Today removing a XDP
memory model, based on page_pool, is only delayed one RCU grace period. This
isn't enough as redirected xdp_frames can still be in-flight on different
queues (remote driver TX, cpumap or veth).

We stress that when drivers use page_pool for DMA-mapping, then they MUST
use one packet per page. This might change in the future, but more work lies
ahead, before we can lift this restriction.

This patchset change the page_pool API to be more strict, as in-flight page
accounting is added.

---

Ilias Apalodimas (2):
      net: page_pool: add helper function to retrieve dma addresses
      net: page_pool: add helper function to unmap dma addresses

Jesper Dangaard Brouer (9):
      xdp: fix leak of IDA cyclic id if rhashtable_insert_slow fails
      xdp: page_pool related fix to cpumap
      veth: use xdp_release_frame for XDP_PASS
      page_pool: introduce page_pool_free and use in mlx5
      mlx5: more strict use of page_pool API
      xdp: tracking page_pool resources and safe removal
      xdp: force mem allocator removal and periodic warning
      xdp: add tracepoints for XDP mem
      page_pool: add tracepoints for page_pool with details need by XDP


 drivers/net/ethernet/mellanox/mlx5/core/en_main.c |   12 +-
 drivers/net/ethernet/mellanox/mlx5/core/en_rx.c   |    3 -
 drivers/net/veth.c                                |    1 
 include/net/page_pool.h                           |   69 +++++++++++-
 include/net/xdp.h                                 |   15 +++
 include/net/xdp_priv.h                            |   23 ++++
 include/trace/events/page_pool.h                  |   87 +++++++++++++++
 include/trace/events/xdp.h                        |  115 ++++++++++++++++++++
 kernel/bpf/cpumap.c                               |    3 +
 net/core/net-traces.c                             |    4 +
 net/core/page_pool.c                              |   87 +++++++++++++--
 net/core/xdp.c                                    |  120 ++++++++++++++++++---
 12 files changed, 494 insertions(+), 45 deletions(-)
 create mode 100644 include/net/xdp_priv.h
 create mode 100644 include/trace/events/page_pool.h

--

[PATCH net-next v1 01/11] net: page_pool: add helper function to retrieve dma addresses

[Jesper Dangaard Brouer]

From: Ilias Apalodimas <ilias.apalodimas@linaro.org>

On a previous patch dma addr was stored in 'struct page'.
Use that to retrieve DMA addresses used by network drivers

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
---
 include/net/page_pool.h |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/net/page_pool.h b/include/net/page_pool.h
index 694d055e01ef..b885d86cb7a1 100644
--- a/include/net/page_pool.h
+++ b/include/net/page_pool.h
@@ -132,6 +132,11 @@ static inline void page_pool_recycle_direct(struct page_pool *pool,
 	__page_pool_put_page(pool, page, true);
 }
 
+static inline dma_addr_t page_pool_get_dma_addr(struct page *page)
+{
+	return page->dma_addr;
+}
+
 static inline bool is_page_pool_compiled_in(void)
 {
 #ifdef CONFIG_PAGE_POOL

[PATCH net-next v1 02/11] net: page_pool: add helper function to unmap dma addresses

[Jesper Dangaard Brouer]

From: Ilias Apalodimas <ilias.apalodimas@linaro.org>

On a previous patch dma addr was stored in 'struct page'.
Use that to unmap DMA addresses used by network drivers

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
---
 include/net/page_pool.h |    1 +
 net/core/page_pool.c    |    7 +++++++
 2 files changed, 8 insertions(+)

diff --git a/include/net/page_pool.h b/include/net/page_pool.h
index b885d86cb7a1..ad218cef88c5 100644
--- a/include/net/page_pool.h
+++ b/include/net/page_pool.h
@@ -110,6 +110,7 @@ static inline struct page *page_pool_dev_alloc_pages(struct page_pool *pool)
 struct page_pool *page_pool_create(const struct page_pool_params *params);
 
 void page_pool_destroy(struct page_pool *pool);
+void page_pool_unmap_page(struct page_pool *pool, struct page *page);
 
 /* Never call this directly, use helpers below */
 void __page_pool_put_page(struct page_pool *pool,
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 5b2252c6d49b..205af7bd6d09 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -190,6 +190,13 @@ static void __page_pool_clean_page(struct page_pool *pool,
 	page->dma_addr = 0;
 }
 
+/* unmap the page and clean our state */
+void page_pool_unmap_page(struct page_pool *pool, struct page *page)
+{
+	__page_pool_clean_page(pool, page);
+}
+EXPORT_SYMBOL(page_pool_unmap_page);
+
 /* Return a page to the page allocator, cleaning up our state */
 static void __page_pool_return_page(struct page_pool *pool, struct page *page)
 {

[PATCH net-next v1 03/11] xdp: fix leak of IDA cyclic id if rhashtable_insert_slow fails

[Jesper Dangaard Brouer]

Fix error handling case, where inserting ID with rhashtable_insert_slow
fails in xdp_rxq_info_reg_mem_model, which leads to never releasing the IDA
ID, as the lookup in xdp_rxq_info_unreg_mem_model fails and thus
ida_simple_remove() is never called.

Fix by releasing ID via ida_simple_remove(), and mark xdp_rxq->mem.id with
zero, which is already checked in xdp_rxq_info_unreg_mem_model().

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
---
 net/core/xdp.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/core/xdp.c b/net/core/xdp.c
index 4b2b194f4f1f..762abeb89847 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -301,6 +301,8 @@ int xdp_rxq_info_reg_mem_model(struct xdp_rxq_info *xdp_rxq,
 	/* Insert allocator into ID lookup table */
 	ptr = rhashtable_insert_slow(mem_id_ht, &id, &xdp_alloc->node);
 	if (IS_ERR(ptr)) {
+		ida_simple_remove(&mem_id_pool, xdp_rxq->mem.id);
+		xdp_rxq->mem.id = 0;
 		errno = PTR_ERR(ptr);
 		goto err;
 	}

[PATCH net-next v1 04/11] xdp: page_pool related fix to cpumap

[Jesper Dangaard Brouer]

When converting an xdp_frame into an SKB, and sending this into the network
stack, then the underlying XDP memory model need to release associated
resources, because the network stack don't have callbacks for XDP memory
models.  The only memory model that needs this is page_pool, when a driver
use the DMA-mapping feature.

Introduce page_pool_release_page(), which basically does the same as
page_pool_unmap_page(). Add xdp_release_frame() as the XDP memory model
interface for calling it, if the memory model match MEM_TYPE_PAGE_POOL, to
save the function call overhead for others. Have cpumap call
xdp_release_frame() before xdp_scrub_frame().

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
---
 include/net/page_pool.h |   15 ++++++++++++++-
 include/net/xdp.h       |   15 +++++++++++++++
 kernel/bpf/cpumap.c     |    3 +++
 net/core/xdp.c          |   15 +++++++++++++++
 4 files changed, 47 insertions(+), 1 deletion(-)

diff --git a/include/net/page_pool.h b/include/net/page_pool.h
index ad218cef88c5..e240fac4c5b9 100644
--- a/include/net/page_pool.h
+++ b/include/net/page_pool.h
@@ -110,7 +110,6 @@ static inline struct page *page_pool_dev_alloc_pages(struct page_pool *pool)
 struct page_pool *page_pool_create(const struct page_pool_params *params);
 
 void page_pool_destroy(struct page_pool *pool);
-void page_pool_unmap_page(struct page_pool *pool, struct page *page);
 
 /* Never call this directly, use helpers below */
 void __page_pool_put_page(struct page_pool *pool,
@@ -133,6 +132,20 @@ static inline void page_pool_recycle_direct(struct page_pool *pool,
 	__page_pool_put_page(pool, page, true);
 }
 
+/* Disconnects a page (from a page_pool).  API users can have a need
+ * to disconnect a page (from a page_pool), to allow it to be used as
+ * a regular page (that will eventually be returned to the normal
+ * page-allocator via put_page).
+ */
+void page_pool_unmap_page(struct page_pool *pool, struct page *page);
+static inline void page_pool_release_page(struct page_pool *pool,
+					  struct page *page)
+{
+#ifdef CONFIG_PAGE_POOL
+	page_pool_unmap_page(pool, page);
+#endif
+}
+
 static inline dma_addr_t page_pool_get_dma_addr(struct page *page)
 {
 	return page->dma_addr;
diff --git a/include/net/xdp.h b/include/net/xdp.h
index 0f25b3675c5c..a06e5f2dfcc5 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h
@@ -129,6 +129,21 @@ void xdp_return_frame(struct xdp_frame *xdpf);
 void xdp_return_frame_rx_napi(struct xdp_frame *xdpf);
 void xdp_return_buff(struct xdp_buff *xdp);
 
+/* When sending xdp_frame into the network stack, then there is no
+ * return point callback, which is needed to release e.g. DMA-mapping
+ * resources with page_pool.  Thus, have explicit function to release
+ * frame resources.
+ */
+void __xdp_release_frame(void *data, struct xdp_mem_info *mem);
+static inline void xdp_release_frame(struct xdp_frame *xdpf)
+{
+	struct xdp_mem_info *mem = &xdpf->mem;
+
+	/* Curr only page_pool needs this */
+	if (mem->type == MEM_TYPE_PAGE_POOL)
+		__xdp_release_frame(xdpf->data, mem);
+}
+
 int xdp_rxq_info_reg(struct xdp_rxq_info *xdp_rxq,
 		     struct net_device *dev, u32 queue_index);
 void xdp_rxq_info_unreg(struct xdp_rxq_info *xdp_rxq);
diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
index cf727d77c6c6..b7a3eab4f7c8 100644
--- a/kernel/bpf/cpumap.c
+++ b/kernel/bpf/cpumap.c
@@ -209,6 +209,9 @@ static struct sk_buff *cpu_map_build_skb(struct bpf_cpu_map_entry *rcpu,
 	 * - RX ring dev queue index	(skb_record_rx_queue)
 	 */
 
+	/* Until page_pool get SKB return path, release DMA here */
+	xdp_release_frame(xdpf);
+
 	/* Allow SKB to reuse area used by xdp_frame */
 	xdp_scrub_frame(xdpf);
 
diff --git a/net/core/xdp.c b/net/core/xdp.c
index 762abeb89847..179d90570afe 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -381,6 +381,21 @@ void xdp_return_buff(struct xdp_buff *xdp)
 }
 EXPORT_SYMBOL_GPL(xdp_return_buff);
 
+/* Only called for MEM_TYPE_PAGE_POOL see xdp.h */
+void __xdp_release_frame(void *data, struct xdp_mem_info *mem)
+{
+	struct xdp_mem_allocator *xa;
+	struct page *page;
+
+	rcu_read_lock();
+	xa = rhashtable_lookup(mem_id_ht, &mem->id, mem_id_rht_params);
+	page = virt_to_head_page(data);
+	if (xa)
+		page_pool_release_page(xa->page_pool, page);
+	rcu_read_unlock();
+}
+EXPORT_SYMBOL_GPL(__xdp_release_frame);
+
 int xdp_attachment_query(struct xdp_attachment_info *info,
 			 struct netdev_bpf *bpf)
 {

[PATCH net-next v1 05/11] veth: use xdp_release_frame for XDP_PASS

[Jesper Dangaard Brouer]

Like cpumap use xdp_release_frame() when an xdp_frame got
converted into an SKB and send towars the network stack.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
---
 drivers/net/veth.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index 52110e54e621..c6916bf1017b 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -547,6 +547,7 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq,
 		goto err;
 	}
 
+	xdp_release_frame(frame);
 	xdp_scrub_frame(frame);
 	skb->protocol = eth_type_trans(skb, rq->dev);
 err:

[PATCH net-next v1 06/11] page_pool: introduce page_pool_free and use in mlx5

[Jesper Dangaard Brouer]

In case driver fails to register the page_pool with XDP return API (via
xdp_rxq_info_reg_mem_model()), then the driver can free the page_pool
resources more directly than calling page_pool_destroy(), which does a
unnecessarily RCU free procedure.

This patch is preparing for removing page_pool_destroy(), from driver
invocation.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
---
 drivers/net/ethernet/mellanox/mlx5/core/en_main.c |    6 +++---
 include/net/page_pool.h                           |   11 +++++++++++
 net/core/page_pool.c                              |   15 +++++++++++----
 3 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
index 457cc39423f2..07de9ca4c53c 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
@@ -545,8 +545,10 @@ static int mlx5e_alloc_rq(struct mlx5e_channel *c,
 	}
 	err = xdp_rxq_info_reg_mem_model(&rq->xdp_rxq,
 					 MEM_TYPE_PAGE_POOL, rq->page_pool);
-	if (err)
+	if (err) {
+		page_pool_free(rq->page_pool);
 		goto err_free;
+	}
 
 	for (i = 0; i < wq_sz; i++) {
 		if (rq->wq_type == MLX5_WQ_TYPE_LINKED_LIST_STRIDING_RQ) {
@@ -611,8 +613,6 @@ static int mlx5e_alloc_rq(struct mlx5e_channel *c,
 	if (rq->xdp_prog)
 		bpf_prog_put(rq->xdp_prog);
 	xdp_rxq_info_unreg(&rq->xdp_rxq);
-	if (rq->page_pool)
-		page_pool_destroy(rq->page_pool);
 	mlx5_wq_destroy(&rq->wq_ctrl);
 
 	return err;
diff --git a/include/net/page_pool.h b/include/net/page_pool.h
index e240fac4c5b9..754d980700df 100644
--- a/include/net/page_pool.h
+++ b/include/net/page_pool.h
@@ -111,6 +111,17 @@ struct page_pool *page_pool_create(const struct page_pool_params *params);
 
 void page_pool_destroy(struct page_pool *pool);
 
+void __page_pool_free(struct page_pool *pool);
+static inline void page_pool_free(struct page_pool *pool)
+{
+	/* When page_pool isn't compiled-in, net/core/xdp.c doesn't
+	 * allow registering MEM_TYPE_PAGE_POOL, but shield linker.
+	 */
+#ifdef CONFIG_PAGE_POOL
+	__page_pool_free(pool);
+#endif
+}
+
 /* Never call this directly, use helpers below */
 void __page_pool_put_page(struct page_pool *pool,
 			  struct page *page, bool allow_direct);
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 205af7bd6d09..41391b5dc14c 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -292,17 +292,24 @@ static void __page_pool_empty_ring(struct page_pool *pool)
 	}
 }
 
+void __page_pool_free(struct page_pool *pool)
+{
+	WARN(pool->alloc.count, "API usage violation");
+	WARN(!ptr_ring_empty(&pool->ring), "ptr_ring is not empty");
+
+	ptr_ring_cleanup(&pool->ring, NULL);
+	kfree(pool);
+}
+EXPORT_SYMBOL(__page_pool_free);
+
 static void __page_pool_destroy_rcu(struct rcu_head *rcu)
 {
 	struct page_pool *pool;
 
 	pool = container_of(rcu, struct page_pool, rcu);
 
-	WARN(pool->alloc.count, "API usage violation");
-
 	__page_pool_empty_ring(pool);
-	ptr_ring_cleanup(&pool->ring, NULL);
-	kfree(pool);
+	__page_pool_free(pool);
 }
 
 /* Cleanup and release resources */

[PATCH net-next v1 07/11] mlx5: more strict use of page_pool API

[Jesper Dangaard Brouer]

The mlx5 driver is using page_pool, but not for DMA-mapping (currently), and
is a little too relaxed about returning or releasing page resources, as it
is not strictly necessary, when not using DMA-mappings.

As this patchset is working towards tracking page_pool resources, to know
about in-flight frames on shutdown. Then fix places where mlx5 leak
page_pool resource.

In case of dma_mapping_error, then recycle into page_pool.

In mlx5e_free_rq() moved the page_pool_destroy() call to after the
mlx5e_page_release() calls, as it is more correct.

In mlx5e_page_release() when no recycle was requested, then release page
from the page_pool, via page_pool_release_page().

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
---
 drivers/net/ethernet/mellanox/mlx5/core/en_main.c |    9 +++++----
 drivers/net/ethernet/mellanox/mlx5/core/en_rx.c   |    3 ++-
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
index 07de9ca4c53c..2f647be292b6 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
@@ -625,10 +625,6 @@ static void mlx5e_free_rq(struct mlx5e_rq *rq)
 	if (rq->xdp_prog)
 		bpf_prog_put(rq->xdp_prog);
 
-	xdp_rxq_info_unreg(&rq->xdp_rxq);
-	if (rq->page_pool)
-		page_pool_destroy(rq->page_pool);
-
 	switch (rq->wq_type) {
 	case MLX5_WQ_TYPE_LINKED_LIST_STRIDING_RQ:
 		kvfree(rq->mpwqe.info);
@@ -645,6 +641,11 @@ static void mlx5e_free_rq(struct mlx5e_rq *rq)
 
 		mlx5e_page_release(rq, dma_info, false);
 	}
+
+	xdp_rxq_info_unreg(&rq->xdp_rxq);
+	if (rq->page_pool)
+		page_pool_destroy(rq->page_pool);
+
 	mlx5_wq_destroy(&rq->wq_ctrl);
 }
 
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
index 13133e7f088e..8331ff2ffdc6 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
@@ -247,7 +247,7 @@ static inline int mlx5e_page_alloc_mapped(struct mlx5e_rq *rq,
 	dma_info->addr = dma_map_page(rq->pdev, dma_info->page, 0,
 				      PAGE_SIZE, rq->buff.map_dir);
 	if (unlikely(dma_mapping_error(rq->pdev, dma_info->addr))) {
-		put_page(dma_info->page);
+		page_pool_recycle_direct(rq->page_pool, dma_info->page);
 		dma_info->page = NULL;
 		return -ENOMEM;
 	}
@@ -271,6 +271,7 @@ void mlx5e_page_release(struct mlx5e_rq *rq, struct mlx5e_dma_info *dma_info,
 		page_pool_recycle_direct(rq->page_pool, dma_info->page);
 	} else {
 		mlx5e_page_dma_unmap(rq, dma_info);
+		page_pool_release_page(rq->page_pool, dma_info->page);
 		put_page(dma_info->page);
 	}
 }

[PATCH net-next v1 08/11] xdp: tracking page_pool resources and safe removal

[Jesper Dangaard Brouer]

This patch is needed before we can allow drivers to use page_pool for
DMA-mappings. Today with page_pool and XDP return API, it is possible to
remove the page_pool object (from rhashtable), while there are still
in-flight packet-pages. This is safely handled via RCU and failed lookups in
__xdp_return() fallback to call put_page(), when page_pool object is gone.
In-case page is still DMA mapped, this will result in page note getting
correctly DMA unmapped.

To solve this, the page_pool is extended with tracking in-flight pages. And
XDP disconnect system queries page_pool and waits, via workqueue, for all
in-flight pages to be returned.

To avoid killing performance when tracking in-flight pages, the implement
use two (unsigned) counters, that in placed on different cache-lines, and
can be used to deduct in-flight packets. This is done by mapping the
unsigned "sequence" counters onto signed Two's complement arithmetic
operations. This is e.g. used by kernel's time_after macros, described in
kernel commit 1ba3aab3033b and 5a581b367b5, and also explained in RFC1982.

The trick is these two incrementing counters only need to be read and
compared, when checking if it's safe to free the page_pool structure. Which
will only happen when driver have disconnected RX/alloc side. Thus, on a
non-fast-path.

It is chosen that page_pool tracking is also enabled for the non-DMA
use-case, as this can be used for statistics later.

After this patch, using page_pool requires more strict resource "release",
e.g. via page_pool_release_page() that was introduced in this patchset, and
previous patches implement/fix this more strict requirement.

Drivers no-longer call page_pool_destroy(). Drivers already call
xdp_rxq_info_unreg() which call xdp_rxq_info_unreg_mem_model(), which will
attempt to disconnect the mem id, and if attempt fails schedule the
disconnect for later via delayed workqueue.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
---
 drivers/net/ethernet/mellanox/mlx5/core/en_main.c |    3 -
 include/net/page_pool.h                           |   41 ++++++++++---
 net/core/page_pool.c                              |   62 +++++++++++++++-----
 net/core/xdp.c                                    |   65 +++++++++++++++++++--
 4 files changed, 136 insertions(+), 35 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
index 2f647be292b6..6c9d4d7defbc 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
@@ -643,9 +643,6 @@ static void mlx5e_free_rq(struct mlx5e_rq *rq)
 	}
 
 	xdp_rxq_info_unreg(&rq->xdp_rxq);
-	if (rq->page_pool)
-		page_pool_destroy(rq->page_pool);
-
 	mlx5_wq_destroy(&rq->wq_ctrl);
 }
 
diff --git a/include/net/page_pool.h b/include/net/page_pool.h
index 754d980700df..f09b3f1994e6 100644
--- a/include/net/page_pool.h
+++ b/include/net/page_pool.h
@@ -16,14 +16,16 @@
  * page_pool_alloc_pages() call.  Drivers should likely use
  * page_pool_dev_alloc_pages() replacing dev_alloc_pages().
  *
- * If page_pool handles DMA mapping (use page->private), then API user
- * is responsible for invoking page_pool_put_page() once.  In-case of
- * elevated refcnt, the DMA state is released, assuming other users of
- * the page will eventually call put_page().
+ * API keeps track of in-flight pages, in-order to let API user know
+ * when it is safe to dealloactor page_pool object.  Thus, API users
+ * must make sure to call page_pool_release_page() when a page is
+ * "leaving" the page_pool.  Or call page_pool_put_page() where
+ * appropiate.  For maintaining correct accounting.
  *
- * If no DMA mapping is done, then it can act as shim-layer that
- * fall-through to alloc_page.  As no state is kept on the page, the
- * regular put_page() call is sufficient.
+ * API user must only call page_pool_put_page() once on a page, as it
+ * will either recycle the page, or in case of elevated refcnt, it
+ * will release the DMA mapping and in-flight state accounting.  We
+ * hope to lift this requirement in the future.
  */
 #ifndef _NET_PAGE_POOL_H
 #define _NET_PAGE_POOL_H
@@ -66,9 +68,10 @@ struct page_pool_params {
 };
 
 struct page_pool {
-	struct rcu_head rcu;
 	struct page_pool_params p;
 
+        u32 pages_state_hold_cnt;
+
 	/*
 	 * Data structure for allocation side
 	 *
@@ -96,6 +99,8 @@ struct page_pool {
 	 * TODO: Implement bulk return pages into this structure.
 	 */
 	struct ptr_ring ring;
+
+	atomic_t pages_state_release_cnt;
 };
 
 struct page *page_pool_alloc_pages(struct page_pool *pool, gfp_t gfp);
@@ -109,8 +114,6 @@ static inline struct page *page_pool_dev_alloc_pages(struct page_pool *pool)
 
 struct page_pool *page_pool_create(const struct page_pool_params *params);
 
-void page_pool_destroy(struct page_pool *pool);
-
 void __page_pool_free(struct page_pool *pool);
 static inline void page_pool_free(struct page_pool *pool)
 {
@@ -143,6 +146,24 @@ static inline void page_pool_recycle_direct(struct page_pool *pool,
 	__page_pool_put_page(pool, page, true);
 }
 
+/* API user MUST have disconnected alloc-side (not allowed to call
+ * page_pool_alloc_pages()) before calling this.  The free-side can
+ * still run concurrently, to handle in-flight packet-pages.
+ *
+ * A request to shutdown can fail (with false) if there are still
+ * in-flight packet-pages.
+ */
+bool __page_pool_request_shutdown(struct page_pool *pool);
+static inline bool page_pool_request_shutdown(struct page_pool *pool)
+{
+	/* When page_pool isn't compiled-in, net/core/xdp.c doesn't
+	 * allow registering MEM_TYPE_PAGE_POOL, but shield linker.
+	 */
+#ifdef CONFIG_PAGE_POOL
+	return __page_pool_request_shutdown(pool);
+#endif
+}
+
 /* Disconnects a page (from a page_pool).  API users can have a need
  * to disconnect a page (from a page_pool), to allow it to be used as
  * a regular page (that will eventually be returned to the normal
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 41391b5dc14c..8679e24fd665 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -43,6 +43,8 @@ static int page_pool_init(struct page_pool *pool,
 	if (ptr_ring_init(&pool->ring, ring_qsize, GFP_KERNEL) < 0)
 		return -ENOMEM;
 
+	atomic_set(&pool->pages_state_release_cnt, 0);
+
 	return 0;
 }
 
@@ -151,6 +153,9 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
 	page->dma_addr = dma;
 
 skip_dma_map:
+	/* Track how many pages are held 'in-flight' */
+	pool->pages_state_hold_cnt++;
+
 	/* When page just alloc'ed is should/must have refcnt 1. */
 	return page;
 }
@@ -173,6 +178,33 @@ struct page *page_pool_alloc_pages(struct page_pool *pool, gfp_t gfp)
 }
 EXPORT_SYMBOL(page_pool_alloc_pages);
 
+/* Calculate distance between two u32 values, valid if distance is below 2^(31)
+ *  https://en.wikipedia.org/wiki/Serial_number_arithmetic#General_Solution
+ */
+#define _distance(a, b)	(s32)((a) - (b))
+
+static s32 page_pool_inflight(struct page_pool *pool)
+{
+	u32 release_cnt = atomic_read(&pool->pages_state_release_cnt);
+	u32 hold_cnt = READ_ONCE(pool->pages_state_hold_cnt);
+	s32 distance;
+
+	distance = _distance(hold_cnt, release_cnt);
+
+	/* TODO: Add tracepoint here */
+	return distance;
+}
+
+static bool __page_pool_safe_to_destroy(struct page_pool *pool)
+{
+	s32 inflight = page_pool_inflight(pool);
+
+	/* The distance should not be able to become negative */
+	WARN(inflight < 0, "Negative(%d) inflight packet-pages", inflight);
+
+	return (inflight == 0);
+}
+
 /* Cleanup page_pool state from page */
 static void __page_pool_clean_page(struct page_pool *pool,
 				   struct page *page)
@@ -180,7 +212,7 @@ static void __page_pool_clean_page(struct page_pool *pool,
 	dma_addr_t dma;
 
 	if (!(pool->p.flags & PP_FLAG_DMA_MAP))
-		return;
+		goto skip_dma_unmap;
 
 	dma = page->dma_addr;
 	/* DMA unmap */
@@ -188,11 +220,16 @@ static void __page_pool_clean_page(struct page_pool *pool,
 			     PAGE_SIZE << pool->p.order, pool->p.dma_dir,
 			     DMA_ATTR_SKIP_CPU_SYNC);
 	page->dma_addr = 0;
+skip_dma_unmap:
+	atomic_inc(&pool->pages_state_release_cnt);
 }
 
 /* unmap the page and clean our state */
 void page_pool_unmap_page(struct page_pool *pool, struct page *page)
 {
+	/* When page is unmapped, this implies page will not be
+	 * returned to page_pool.
+	 */
 	__page_pool_clean_page(pool, page);
 }
 EXPORT_SYMBOL(page_pool_unmap_page);
@@ -201,6 +238,7 @@ EXPORT_SYMBOL(page_pool_unmap_page);
 static void __page_pool_return_page(struct page_pool *pool, struct page *page)
 {
 	__page_pool_clean_page(pool, page);
+
 	put_page(page);
 	/* An optimization would be to call __free_pages(page, pool->p.order)
 	 * knowing page is not part of page-cache (thus avoiding a
@@ -296,24 +334,17 @@ void __page_pool_free(struct page_pool *pool)
 {
 	WARN(pool->alloc.count, "API usage violation");
 	WARN(!ptr_ring_empty(&pool->ring), "ptr_ring is not empty");
+	WARN(!__page_pool_safe_to_destroy(pool), "still in-flight pages");
 
 	ptr_ring_cleanup(&pool->ring, NULL);
 	kfree(pool);
 }
 EXPORT_SYMBOL(__page_pool_free);
 
-static void __page_pool_destroy_rcu(struct rcu_head *rcu)
-{
-	struct page_pool *pool;
-
-	pool = container_of(rcu, struct page_pool, rcu);
-
-	__page_pool_empty_ring(pool);
-	__page_pool_free(pool);
-}
-
-/* Cleanup and release resources */
-void page_pool_destroy(struct page_pool *pool)
+/* Request to shutdown: release pages cached by page_pool, and check
+ * for in-flight pages
+ */
+bool __page_pool_request_shutdown(struct page_pool *pool)
 {
 	struct page *page;
 
@@ -331,7 +362,6 @@ void page_pool_destroy(struct page_pool *pool)
 	 */
 	__page_pool_empty_ring(pool);
 
-	/* An xdp_mem_allocator can still ref page_pool pointer */
-	call_rcu(&pool->rcu, __page_pool_destroy_rcu);
+	return __page_pool_safe_to_destroy(pool);
 }
-EXPORT_SYMBOL(page_pool_destroy);
+EXPORT_SYMBOL(__page_pool_request_shutdown);
diff --git a/net/core/xdp.c b/net/core/xdp.c
index 179d90570afe..2b7bad227030 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -38,6 +38,7 @@ struct xdp_mem_allocator {
 	};
 	struct rhash_head node;
 	struct rcu_head rcu;
+	struct delayed_work defer_wq;
 };
 
 static u32 xdp_mem_id_hashfn(const void *data, u32 len, u32 seed)
@@ -79,13 +80,13 @@ static void __xdp_mem_allocator_rcu_free(struct rcu_head *rcu)
 
 	xa = container_of(rcu, struct xdp_mem_allocator, rcu);
 
+	/* Allocator have indicated safe to remove before this is called */
+	if (xa->mem.type == MEM_TYPE_PAGE_POOL)
+		page_pool_free(xa->page_pool);
+
 	/* Allow this ID to be reused */
 	ida_simple_remove(&mem_id_pool, xa->mem.id);
 
-	/* Notice, driver is expected to free the *allocator,
-	 * e.g. page_pool, and MUST also use RCU free.
-	 */
-
 	/* Poison memory */
 	xa->mem.id = 0xFFFF;
 	xa->mem.type = 0xF0F0;
@@ -94,6 +95,46 @@ static void __xdp_mem_allocator_rcu_free(struct rcu_head *rcu)
 	kfree(xa);
 }
 
+bool __mem_id_disconnect(int id)
+{
+	struct xdp_mem_allocator *xa;
+	bool safe_to_remove = true;
+
+	mutex_lock(&mem_id_lock);
+
+	xa = rhashtable_lookup_fast(mem_id_ht, &id, mem_id_rht_params);
+	if (!xa) {
+		mutex_unlock(&mem_id_lock);
+		WARN(1, "Request remove non-existing id(%d), driver bug?", id);
+		return true;
+	}
+
+	/* Detects in-flight packet-pages for page_pool */
+	if (xa->mem.type == MEM_TYPE_PAGE_POOL)
+		safe_to_remove = page_pool_request_shutdown(xa->page_pool);
+
+	if (safe_to_remove &&
+	    !rhashtable_remove_fast(mem_id_ht, &xa->node, mem_id_rht_params))
+		call_rcu(&xa->rcu, __xdp_mem_allocator_rcu_free);
+
+	mutex_unlock(&mem_id_lock);
+	return safe_to_remove;
+}
+
+#define DEFER_TIME (msecs_to_jiffies(1000))
+
+static void mem_id_disconnect_defer_retry(struct work_struct *wq)
+{
+	struct delayed_work *dwq = to_delayed_work(wq);
+	struct xdp_mem_allocator *xa = container_of(dwq, typeof(*xa), defer_wq);
+
+	if (__mem_id_disconnect(xa->mem.id))
+		return;
+
+	/* Still not ready to be disconnected, retry later */
+	schedule_delayed_work(&xa->defer_wq, DEFER_TIME);
+}
+
 void xdp_rxq_info_unreg_mem_model(struct xdp_rxq_info *xdp_rxq)
 {
 	struct xdp_mem_allocator *xa;
@@ -112,16 +153,28 @@ void xdp_rxq_info_unreg_mem_model(struct xdp_rxq_info *xdp_rxq)
 	if (id == 0)
 		return;
 
+	if (__mem_id_disconnect(id))
+		return;
+
+	/* Could not disconnect, defer new disconnect attempt to later */
 	mutex_lock(&mem_id_lock);
 
 	xa = rhashtable_lookup_fast(mem_id_ht, &id, mem_id_rht_params);
-	if (xa && !rhashtable_remove_fast(mem_id_ht, &xa->node, mem_id_rht_params))
-		call_rcu(&xa->rcu, __xdp_mem_allocator_rcu_free);
+	if (!xa) {
+		mutex_unlock(&mem_id_lock);
+		return;
+	}
 
+	INIT_DELAYED_WORK(&xa->defer_wq, mem_id_disconnect_defer_retry);
 	mutex_unlock(&mem_id_lock);
+	schedule_delayed_work(&xa->defer_wq, DEFER_TIME);
 }
 EXPORT_SYMBOL_GPL(xdp_rxq_info_unreg_mem_model);
 
+/* This unregister operation will also cleanup and destroy the
+ * allocator. The page_pool_free() operation is first called when it's
+ * safe to remove, possibly deferred to a workqueue.
+ */
 void xdp_rxq_info_unreg(struct xdp_rxq_info *xdp_rxq)
 {
 	/* Simplify driver cleanup code paths, allow unreg "unused" */

Re: [PATCH net-next v1 08/11] xdp: tracking page_pool resources and safe removal

[Ilias Apalodimas]

Hi Jesper, 

Minot nit picks mostly,

On Thu, Jun 13, 2019 at 08:28:42PM +0200, Jesper Dangaard Brouer wrote:
> This patch is needed before we can allow drivers to use page_pool for
> DMA-mappings. Today with page_pool and XDP return API, it is possible to
> remove the page_pool object (from rhashtable), while there are still
> in-flight packet-pages. This is safely handled via RCU and failed lookups in
> __xdp_return() fallback to call put_page(), when page_pool object is gone.
> In-case page is still DMA mapped, this will result in page note getting
> correctly DMA unmapped.
> 
> To solve this, the page_pool is extended with tracking in-flight pages. And
> XDP disconnect system queries page_pool and waits, via workqueue, for all
> in-flight pages to be returned.
> 
> To avoid killing performance when tracking in-flight pages, the implement
> use two (unsigned) counters, that in placed on different cache-lines, and
> can be used to deduct in-flight packets. This is done by mapping the
> unsigned "sequence" counters onto signed Two's complement arithmetic
> operations. This is e.g. used by kernel's time_after macros, described in
> kernel commit 1ba3aab3033b and 5a581b367b5, and also explained in RFC1982.
> 
> The trick is these two incrementing counters only need to be read and
> compared, when checking if it's safe to free the page_pool structure. Which
> will only happen when driver have disconnected RX/alloc side. Thus, on a
> non-fast-path.
> 
> It is chosen that page_pool tracking is also enabled for the non-DMA
> use-case, as this can be used for statistics later.
> 
> After this patch, using page_pool requires more strict resource "release",
> e.g. via page_pool_release_page() that was introduced in this patchset, and
> previous patches implement/fix this more strict requirement.
> 
> Drivers no-longer call page_pool_destroy(). Drivers already call
> xdp_rxq_info_unreg() which call xdp_rxq_info_unreg_mem_model(), which will
> attempt to disconnect the mem id, and if attempt fails schedule the
> disconnect for later via delayed workqueue.
> 
> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
> ---
>  drivers/net/ethernet/mellanox/mlx5/core/en_main.c |    3 -
>  include/net/page_pool.h                           |   41 ++++++++++---
>  net/core/page_pool.c                              |   62 +++++++++++++++-----
>  net/core/xdp.c                                    |   65 +++++++++++++++++++--
>  4 files changed, 136 insertions(+), 35 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> index 2f647be292b6..6c9d4d7defbc 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> @@ -643,9 +643,6 @@ static void mlx5e_free_rq(struct mlx5e_rq *rq)
>  	}
>  
>  	xdp_rxq_info_unreg(&rq->xdp_rxq);
> -	if (rq->page_pool)
> -		page_pool_destroy(rq->page_pool);
> -
>  	mlx5_wq_destroy(&rq->wq_ctrl);
>  }
>  
> diff --git a/include/net/page_pool.h b/include/net/page_pool.h
> index 754d980700df..f09b3f1994e6 100644
> --- a/include/net/page_pool.h
> +++ b/include/net/page_pool.h
> @@ -16,14 +16,16 @@
>   * page_pool_alloc_pages() call.  Drivers should likely use
>   * page_pool_dev_alloc_pages() replacing dev_alloc_pages().
>   *
> - * If page_pool handles DMA mapping (use page->private), then API user
> - * is responsible for invoking page_pool_put_page() once.  In-case of
> - * elevated refcnt, the DMA state is released, assuming other users of
> - * the page will eventually call put_page().
> + * API keeps track of in-flight pages, in-order to let API user know
> + * when it is safe to dealloactor page_pool object.  Thus, API users
> + * must make sure to call page_pool_release_page() when a page is
> + * "leaving" the page_pool.  Or call page_pool_put_page() where
> + * appropiate.  For maintaining correct accounting.
>   *
> - * If no DMA mapping is done, then it can act as shim-layer that
> - * fall-through to alloc_page.  As no state is kept on the page, the
> - * regular put_page() call is sufficient.
> + * API user must only call page_pool_put_page() once on a page, as it
> + * will either recycle the page, or in case of elevated refcnt, it
> + * will release the DMA mapping and in-flight state accounting.  We
> + * hope to lift this requirement in the future.
>   */
>  #ifndef _NET_PAGE_POOL_H
>  #define _NET_PAGE_POOL_H
> @@ -66,9 +68,10 @@ struct page_pool_params {
>  };
>  
>  struct page_pool {
> -	struct rcu_head rcu;
>  	struct page_pool_params p;
>  
> +        u32 pages_state_hold_cnt;
Maybe mention the different cache-line placement for pages_state_hold_cnt and 
pages_state_release_cnt as described in the commit message for future editors?
> +
>  	/*
>  	 * Data structure for allocation side
>  	 *
> @@ -96,6 +99,8 @@ struct page_pool {
>  	 * TODO: Implement bulk return pages into this structure.
>  	 */
>  	struct ptr_ring ring;
> +
> +	atomic_t pages_state_release_cnt;
As we discussed this can change to per-cpu release variables if atomics end up
hurting performance. I am fine with leaving this as-is and optimize if we spot
any bottlenecks

>  };
>  
>  struct page *page_pool_alloc_pages(struct page_pool *pool, gfp_t gfp);
> @@ -109,8 +114,6 @@ static inline struct page *page_pool_dev_alloc_pages(struct page_pool *pool)
>  
>  struct page_pool *page_pool_create(const struct page_pool_params *params);
>  
> -void page_pool_destroy(struct page_pool *pool);
> -
>  void __page_pool_free(struct page_pool *pool);
>  static inline void page_pool_free(struct page_pool *pool)
>  {
> @@ -143,6 +146,24 @@ static inline void page_pool_recycle_direct(struct page_pool *pool,
>  	__page_pool_put_page(pool, page, true);
>  }
>  
> +/* API user MUST have disconnected alloc-side (not allowed to call
> + * page_pool_alloc_pages()) before calling this.  The free-side can
> + * still run concurrently, to handle in-flight packet-pages.
> + *
> + * A request to shutdown can fail (with false) if there are still
> + * in-flight packet-pages.
> + */
> +bool __page_pool_request_shutdown(struct page_pool *pool);
> +static inline bool page_pool_request_shutdown(struct page_pool *pool)
> +{
> +	/* When page_pool isn't compiled-in, net/core/xdp.c doesn't
> +	 * allow registering MEM_TYPE_PAGE_POOL, but shield linker.
> +	 */
> +#ifdef CONFIG_PAGE_POOL
> +	return __page_pool_request_shutdown(pool);
> +#endif
> +}
> +
>  /* Disconnects a page (from a page_pool).  API users can have a need
>   * to disconnect a page (from a page_pool), to allow it to be used as
>   * a regular page (that will eventually be returned to the normal
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index 41391b5dc14c..8679e24fd665 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -43,6 +43,8 @@ static int page_pool_init(struct page_pool *pool,
>  	if (ptr_ring_init(&pool->ring, ring_qsize, GFP_KERNEL) < 0)
>  		return -ENOMEM;
>  
> +	atomic_set(&pool->pages_state_release_cnt, 0);
> +
>  	return 0;
>  }
>  
> @@ -151,6 +153,9 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
>  	page->dma_addr = dma;
>  
>  skip_dma_map:
> +	/* Track how many pages are held 'in-flight' */
> +	pool->pages_state_hold_cnt++;
> +
>  	/* When page just alloc'ed is should/must have refcnt 1. */
>  	return page;
>  }
> @@ -173,6 +178,33 @@ struct page *page_pool_alloc_pages(struct page_pool *pool, gfp_t gfp)
>  }
>  EXPORT_SYMBOL(page_pool_alloc_pages);
>  
> +/* Calculate distance between two u32 values, valid if distance is below 2^(31)
> + *  https://en.wikipedia.org/wiki/Serial_number_arithmetic#General_Solution
> + */
> +#define _distance(a, b)	(s32)((a) - (b))
> +
> +static s32 page_pool_inflight(struct page_pool *pool)
> +{
> +	u32 release_cnt = atomic_read(&pool->pages_state_release_cnt);
> +	u32 hold_cnt = READ_ONCE(pool->pages_state_hold_cnt);
> +	s32 distance;
> +
> +	distance = _distance(hold_cnt, release_cnt);
> +
> +	/* TODO: Add tracepoint here */
> +	return distance;
> +}
> +
> +static bool __page_pool_safe_to_destroy(struct page_pool *pool)
> +{
> +	s32 inflight = page_pool_inflight(pool);
> +
> +	/* The distance should not be able to become negative */
> +	WARN(inflight < 0, "Negative(%d) inflight packet-pages", inflight);
> +
> +	return (inflight == 0);
> +}
> +
>  /* Cleanup page_pool state from page */
>  static void __page_pool_clean_page(struct page_pool *pool,
>  				   struct page *page)
> @@ -180,7 +212,7 @@ static void __page_pool_clean_page(struct page_pool *pool,
>  	dma_addr_t dma;
>  
>  	if (!(pool->p.flags & PP_FLAG_DMA_MAP))
> -		return;
> +		goto skip_dma_unmap;
>  
>  	dma = page->dma_addr;
>  	/* DMA unmap */
> @@ -188,11 +220,16 @@ static void __page_pool_clean_page(struct page_pool *pool,
>  			     PAGE_SIZE << pool->p.order, pool->p.dma_dir,
>  			     DMA_ATTR_SKIP_CPU_SYNC);
>  	page->dma_addr = 0;
> +skip_dma_unmap:
> +	atomic_inc(&pool->pages_state_release_cnt);
>  }
>  
>  /* unmap the page and clean our state */
>  void page_pool_unmap_page(struct page_pool *pool, struct page *page)
>  {
> +	/* When page is unmapped, this implies page will not be
> +	 * returned to page_pool.
> +	 */
>  	__page_pool_clean_page(pool, page);
>  }
>  EXPORT_SYMBOL(page_pool_unmap_page);
> @@ -201,6 +238,7 @@ EXPORT_SYMBOL(page_pool_unmap_page);
>  static void __page_pool_return_page(struct page_pool *pool, struct page *page)
>  {
>  	__page_pool_clean_page(pool, page);
> +
>  	put_page(page);
>  	/* An optimization would be to call __free_pages(page, pool->p.order)
>  	 * knowing page is not part of page-cache (thus avoiding a
> @@ -296,24 +334,17 @@ void __page_pool_free(struct page_pool *pool)
>  {
>  	WARN(pool->alloc.count, "API usage violation");
>  	WARN(!ptr_ring_empty(&pool->ring), "ptr_ring is not empty");
> +	WARN(!__page_pool_safe_to_destroy(pool), "still in-flight pages");
>  
>  	ptr_ring_cleanup(&pool->ring, NULL);
>  	kfree(pool);
>  }
>  EXPORT_SYMBOL(__page_pool_free);
>  
> -static void __page_pool_destroy_rcu(struct rcu_head *rcu)
> -{
> -	struct page_pool *pool;
> -
> -	pool = container_of(rcu, struct page_pool, rcu);
> -
> -	__page_pool_empty_ring(pool);
> -	__page_pool_free(pool);
> -}
> -
> -/* Cleanup and release resources */
> -void page_pool_destroy(struct page_pool *pool)
> +/* Request to shutdown: release pages cached by page_pool, and check
> + * for in-flight pages
> + */
> +bool __page_pool_request_shutdown(struct page_pool *pool)
>  {
>  	struct page *page;
>  
> @@ -331,7 +362,6 @@ void page_pool_destroy(struct page_pool *pool)
>  	 */
>  	__page_pool_empty_ring(pool);
>  
> -	/* An xdp_mem_allocator can still ref page_pool pointer */
> -	call_rcu(&pool->rcu, __page_pool_destroy_rcu);
> +	return __page_pool_safe_to_destroy(pool);
>  }
> -EXPORT_SYMBOL(page_pool_destroy);
> +EXPORT_SYMBOL(__page_pool_request_shutdown);
> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index 179d90570afe..2b7bad227030 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -38,6 +38,7 @@ struct xdp_mem_allocator {
>  	};
>  	struct rhash_head node;
>  	struct rcu_head rcu;
> +	struct delayed_work defer_wq;
>  };
>  
>  static u32 xdp_mem_id_hashfn(const void *data, u32 len, u32 seed)
> @@ -79,13 +80,13 @@ static void __xdp_mem_allocator_rcu_free(struct rcu_head *rcu)
>  
>  	xa = container_of(rcu, struct xdp_mem_allocator, rcu);
>  
> +	/* Allocator have indicated safe to remove before this is called */
> +	if (xa->mem.type == MEM_TYPE_PAGE_POOL)
> +		page_pool_free(xa->page_pool);
> +
>  	/* Allow this ID to be reused */
>  	ida_simple_remove(&mem_id_pool, xa->mem.id);
>  
> -	/* Notice, driver is expected to free the *allocator,
> -	 * e.g. page_pool, and MUST also use RCU free.
> -	 */
> -
>  	/* Poison memory */
>  	xa->mem.id = 0xFFFF;
>  	xa->mem.type = 0xF0F0;
> @@ -94,6 +95,46 @@ static void __xdp_mem_allocator_rcu_free(struct rcu_head *rcu)
>  	kfree(xa);
>  }
>  
> +bool __mem_id_disconnect(int id)
> +{
> +	struct xdp_mem_allocator *xa;
> +	bool safe_to_remove = true;
> +
> +	mutex_lock(&mem_id_lock);
> +
> +	xa = rhashtable_lookup_fast(mem_id_ht, &id, mem_id_rht_params);
> +	if (!xa) {
> +		mutex_unlock(&mem_id_lock);
> +		WARN(1, "Request remove non-existing id(%d), driver bug?", id);
> +		return true;
> +	}
> +
> +	/* Detects in-flight packet-pages for page_pool */
> +	if (xa->mem.type == MEM_TYPE_PAGE_POOL)
> +		safe_to_remove = page_pool_request_shutdown(xa->page_pool);
> +
> +	if (safe_to_remove &&
> +	    !rhashtable_remove_fast(mem_id_ht, &xa->node, mem_id_rht_params))
> +		call_rcu(&xa->rcu, __xdp_mem_allocator_rcu_free);
> +
> +	mutex_unlock(&mem_id_lock);
> +	return safe_to_remove;
> +}
> +
> +#define DEFER_TIME (msecs_to_jiffies(1000))
> +
> +static void mem_id_disconnect_defer_retry(struct work_struct *wq)
> +{
> +	struct delayed_work *dwq = to_delayed_work(wq);
> +	struct xdp_mem_allocator *xa = container_of(dwq, typeof(*xa), defer_wq);
> +
> +	if (__mem_id_disconnect(xa->mem.id))
> +		return;
> +
> +	/* Still not ready to be disconnected, retry later */
> +	schedule_delayed_work(&xa->defer_wq, DEFER_TIME);
> +}
> +
>  void xdp_rxq_info_unreg_mem_model(struct xdp_rxq_info *xdp_rxq)
Again as we already discussed, the naming for destroying a registered page_pool
is mixed with xdp_ prefixes. That's fine but we'll need to document it properly
once real drivers start using this

>  {
>  	struct xdp_mem_allocator *xa;
> @@ -112,16 +153,28 @@ void xdp_rxq_info_unreg_mem_model(struct xdp_rxq_info *xdp_rxq)
>  	if (id == 0)
>  		return;
>  
> +	if (__mem_id_disconnect(id))
> +		return;
> +
> +	/* Could not disconnect, defer new disconnect attempt to later */
>  	mutex_lock(&mem_id_lock);
>  
>  	xa = rhashtable_lookup_fast(mem_id_ht, &id, mem_id_rht_params);
> -	if (xa && !rhashtable_remove_fast(mem_id_ht, &xa->node, mem_id_rht_params))
> -		call_rcu(&xa->rcu, __xdp_mem_allocator_rcu_free);
> +	if (!xa) {
> +		mutex_unlock(&mem_id_lock);
> +		return;
> +	}
>  
> +	INIT_DELAYED_WORK(&xa->defer_wq, mem_id_disconnect_defer_retry);
>  	mutex_unlock(&mem_id_lock);
> +	schedule_delayed_work(&xa->defer_wq, DEFER_TIME);
>  }
>  EXPORT_SYMBOL_GPL(xdp_rxq_info_unreg_mem_model);
>  
> +/* This unregister operation will also cleanup and destroy the
> + * allocator. The page_pool_free() operation is first called when it's
> + * safe to remove, possibly deferred to a workqueue.
> + */
>  void xdp_rxq_info_unreg(struct xdp_rxq_info *xdp_rxq)
>  {
>  	/* Simplify driver cleanup code paths, allow unreg "unused" */
> 

Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>

Re: [PATCH net-next v1 08/11] xdp: tracking page_pool resources and safe removal

[Ivan Khoronzhuk]

On Thu, Jun 13, 2019 at 08:28:42PM +0200, Jesper Dangaard Brouer wrote:
Hi, Jesper

>This patch is needed before we can allow drivers to use page_pool for
>DMA-mappings. Today with page_pool and XDP return API, it is possible to
>remove the page_pool object (from rhashtable), while there are still
>in-flight packet-pages. This is safely handled via RCU and failed lookups in
>__xdp_return() fallback to call put_page(), when page_pool object is gone.
>In-case page is still DMA mapped, this will result in page note getting
>correctly DMA unmapped.
>
>To solve this, the page_pool is extended with tracking in-flight pages. And
>XDP disconnect system queries page_pool and waits, via workqueue, for all
>in-flight pages to be returned.
>
>To avoid killing performance when tracking in-flight pages, the implement
>use two (unsigned) counters, that in placed on different cache-lines, and
>can be used to deduct in-flight packets. This is done by mapping the
>unsigned "sequence" counters onto signed Two's complement arithmetic
>operations. This is e.g. used by kernel's time_after macros, described in
>kernel commit 1ba3aab3033b and 5a581b367b5, and also explained in RFC1982.
>
>The trick is these two incrementing counters only need to be read and
>compared, when checking if it's safe to free the page_pool structure. Which
>will only happen when driver have disconnected RX/alloc side. Thus, on a
>non-fast-path.
>
>It is chosen that page_pool tracking is also enabled for the non-DMA
>use-case, as this can be used for statistics later.
>
>After this patch, using page_pool requires more strict resource "release",
>e.g. via page_pool_release_page() that was introduced in this patchset, and
>previous patches implement/fix this more strict requirement.
>
>Drivers no-longer call page_pool_destroy(). Drivers already call
>xdp_rxq_info_unreg() which call xdp_rxq_info_unreg_mem_model(), which will
>attempt to disconnect the mem id, and if attempt fails schedule the
>disconnect for later via delayed workqueue.
>
>Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
>---
> drivers/net/ethernet/mellanox/mlx5/core/en_main.c |    3 -
> include/net/page_pool.h                           |   41 ++++++++++---
> net/core/page_pool.c                              |   62 +++++++++++++++-----
> net/core/xdp.c                                    |   65 +++++++++++++++++++--
> 4 files changed, 136 insertions(+), 35 deletions(-)
>
>diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>index 2f647be292b6..6c9d4d7defbc 100644
>--- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c

[...]

>--- a/net/core/xdp.c
>+++ b/net/core/xdp.c
>@@ -38,6 +38,7 @@ struct xdp_mem_allocator {
> 	};
> 	struct rhash_head node;
> 	struct rcu_head rcu;
>+	struct delayed_work defer_wq;
> };
>
> static u32 xdp_mem_id_hashfn(const void *data, u32 len, u32 seed)
>@@ -79,13 +80,13 @@ static void __xdp_mem_allocator_rcu_free(struct rcu_head *rcu)
>
> 	xa = container_of(rcu, struct xdp_mem_allocator, rcu);
>
>+	/* Allocator have indicated safe to remove before this is called */
>+	if (xa->mem.type == MEM_TYPE_PAGE_POOL)
>+		page_pool_free(xa->page_pool);
>+

What would you recommend to do for the following situation:

Same receive queue is shared between 2 network devices. The receive ring is
filled by pages from page_pool, but you don't know the actual port (ndev)
filling this ring, because a device is recognized only after packet is received.

The API is so that xdp rxq is bind to network device, each frame has reference
on it, so rxq ndev must be static. That means each netdev has it's own rxq
instance even no need in it. Thus, after your changes, page must be returned to
the pool it was taken from, or released from old pool and recycled in new one
somehow.

And that is inconvenience at least. It's hard to move pages between pools w/o
performance penalty. No way to use common pool either, as unreg_rxq now drops
the pool and 2 rxqa can't reference same pool.

-- 
Regards,
Ivan Khoronzhuk

Re: [PATCH net-next v1 08/11] xdp: tracking page_pool resources and safe removal

[Tariq Toukan]

On 6/15/2019 12:33 PM, Ivan Khoronzhuk wrote:
> On Thu, Jun 13, 2019 at 08:28:42PM +0200, Jesper Dangaard Brouer wrote:
> Hi, Jesper
> 
>> This patch is needed before we can allow drivers to use page_pool for
>> DMA-mappings. Today with page_pool and XDP return API, it is possible to
>> remove the page_pool object (from rhashtable), while there are still
>> in-flight packet-pages. This is safely handled via RCU and failed 
>> lookups in
>> __xdp_return() fallback to call put_page(), when page_pool object is 
>> gone.
>> In-case page is still DMA mapped, this will result in page note getting
>> correctly DMA unmapped.
>>
>> To solve this, the page_pool is extended with tracking in-flight 
>> pages. And
>> XDP disconnect system queries page_pool and waits, via workqueue, for all
>> in-flight pages to be returned.
>>
>> To avoid killing performance when tracking in-flight pages, the implement
>> use two (unsigned) counters, that in placed on different cache-lines, and
>> can be used to deduct in-flight packets. This is done by mapping the
>> unsigned "sequence" counters onto signed Two's complement arithmetic
>> operations. This is e.g. used by kernel's time_after macros, described in
>> kernel commit 1ba3aab3033b and 5a581b367b5, and also explained in 
>> RFC1982.
>>
>> The trick is these two incrementing counters only need to be read and
>> compared, when checking if it's safe to free the page_pool structure. 
>> Which
>> will only happen when driver have disconnected RX/alloc side. Thus, on a
>> non-fast-path.
>>
>> It is chosen that page_pool tracking is also enabled for the non-DMA
>> use-case, as this can be used for statistics later.
>>
>> After this patch, using page_pool requires more strict resource 
>> "release",
>> e.g. via page_pool_release_page() that was introduced in this 
>> patchset, and
>> previous patches implement/fix this more strict requirement.
>>
>> Drivers no-longer call page_pool_destroy(). Drivers already call
>> xdp_rxq_info_unreg() which call xdp_rxq_info_unreg_mem_model(), which 
>> will
>> attempt to disconnect the mem id, and if attempt fails schedule the
>> disconnect for later via delayed workqueue.
>>
>> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
>> ---
>> drivers/net/ethernet/mellanox/mlx5/core/en_main.c |    3 -
>> include/net/page_pool.h                           |   41 ++++++++++---
>> net/core/page_pool.c                              |   62 
>> +++++++++++++++-----
>> net/core/xdp.c                                    |   65 
>> +++++++++++++++++++--
>> 4 files changed, 136 insertions(+), 35 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c 
>> b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>> index 2f647be292b6..6c9d4d7defbc 100644
>> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> 
> [...]
> 
>> --- a/net/core/xdp.c
>> +++ b/net/core/xdp.c
>> @@ -38,6 +38,7 @@ struct xdp_mem_allocator {
>>     };
>>     struct rhash_head node;
>>     struct rcu_head rcu;
>> +    struct delayed_work defer_wq;
>> };
>>
>> static u32 xdp_mem_id_hashfn(const void *data, u32 len, u32 seed)
>> @@ -79,13 +80,13 @@ static void __xdp_mem_allocator_rcu_free(struct 
>> rcu_head *rcu)
>>
>>     xa = container_of(rcu, struct xdp_mem_allocator, rcu);
>>
>> +    /* Allocator have indicated safe to remove before this is called */
>> +    if (xa->mem.type == MEM_TYPE_PAGE_POOL)
>> +        page_pool_free(xa->page_pool);
>> +
> 
> What would you recommend to do for the following situation:
> 
> Same receive queue is shared between 2 network devices. The receive ring is
> filled by pages from page_pool, but you don't know the actual port (ndev)
> filling this ring, because a device is recognized only after packet is 
> received.
> 
> The API is so that xdp rxq is bind to network device, each frame has 
> reference
> on it, so rxq ndev must be static. That means each netdev has it's own rxq
> instance even no need in it. Thus, after your changes, page must be 
> returned to
> the pool it was taken from, or released from old pool and recycled in 
> new one
> somehow.
> 
> And that is inconvenience at least. It's hard to move pages between 
> pools w/o
> performance penalty. No way to use common pool either, as unreg_rxq now 
> drops
> the pool and 2 rxqa can't reference same pool.
> 

Within the single netdev, separate page_pool instances are anyway 
created for different RX rings, working under different NAPI's.
So I don't understand your comment above about breaking some 
multi-netdev pool sharing use case...

Tariq

Re: [PATCH net-next v1 08/11] xdp: tracking page_pool resources and safe removal

[Ivan Khoronzhuk]

On Sun, Jun 16, 2019 at 10:56:25AM +0000, Tariq Toukan wrote:

Hi Tariq

>
>
>On 6/15/2019 12:33 PM, Ivan Khoronzhuk wrote:
>> On Thu, Jun 13, 2019 at 08:28:42PM +0200, Jesper Dangaard Brouer wrote:
>> Hi, Jesper
>>
>>> This patch is needed before we can allow drivers to use page_pool for
>>> DMA-mappings. Today with page_pool and XDP return API, it is possible to
>>> remove the page_pool object (from rhashtable), while there are still
>>> in-flight packet-pages. This is safely handled via RCU and failed
>>> lookups in
>>> __xdp_return() fallback to call put_page(), when page_pool object is
>>> gone.
>>> In-case page is still DMA mapped, this will result in page note getting
>>> correctly DMA unmapped.
>>>
>>> To solve this, the page_pool is extended with tracking in-flight
>>> pages. And
>>> XDP disconnect system queries page_pool and waits, via workqueue, for all
>>> in-flight pages to be returned.
>>>
>>> To avoid killing performance when tracking in-flight pages, the implement
>>> use two (unsigned) counters, that in placed on different cache-lines, and
>>> can be used to deduct in-flight packets. This is done by mapping the
>>> unsigned "sequence" counters onto signed Two's complement arithmetic
>>> operations. This is e.g. used by kernel's time_after macros, described in
>>> kernel commit 1ba3aab3033b and 5a581b367b5, and also explained in
>>> RFC1982.
>>>
>>> The trick is these two incrementing counters only need to be read and
>>> compared, when checking if it's safe to free the page_pool structure.
>>> Which
>>> will only happen when driver have disconnected RX/alloc side. Thus, on a
>>> non-fast-path.
>>>
>>> It is chosen that page_pool tracking is also enabled for the non-DMA
>>> use-case, as this can be used for statistics later.
>>>
>>> After this patch, using page_pool requires more strict resource
>>> "release",
>>> e.g. via page_pool_release_page() that was introduced in this
>>> patchset, and
>>> previous patches implement/fix this more strict requirement.
>>>
>>> Drivers no-longer call page_pool_destroy(). Drivers already call
>>> xdp_rxq_info_unreg() which call xdp_rxq_info_unreg_mem_model(), which
>>> will
>>> attempt to disconnect the mem id, and if attempt fails schedule the
>>> disconnect for later via delayed workqueue.
>>>
>>> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
>>> ---
>>> drivers/net/ethernet/mellanox/mlx5/core/en_main.c |    3 -
>>> include/net/page_pool.h                           |   41 ++++++++++---
>>> net/core/page_pool.c                              |   62
>>> +++++++++++++++-----
>>> net/core/xdp.c                                    |   65
>>> +++++++++++++++++++--
>>> 4 files changed, 136 insertions(+), 35 deletions(-)
>>>
>>> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>>> b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>>> index 2f647be292b6..6c9d4d7defbc 100644
>>> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>>> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>>
>> [...]
>>
>>> --- a/net/core/xdp.c
>>> +++ b/net/core/xdp.c
>>> @@ -38,6 +38,7 @@ struct xdp_mem_allocator {
>>>     };
>>>     struct rhash_head node;
>>>     struct rcu_head rcu;
>>> +    struct delayed_work defer_wq;
>>> };
>>>
>>> static u32 xdp_mem_id_hashfn(const void *data, u32 len, u32 seed)
>>> @@ -79,13 +80,13 @@ static void __xdp_mem_allocator_rcu_free(struct
>>> rcu_head *rcu)
>>>
>>>     xa = container_of(rcu, struct xdp_mem_allocator, rcu);
>>>
>>> +    /* Allocator have indicated safe to remove before this is called */
>>> +    if (xa->mem.type == MEM_TYPE_PAGE_POOL)
>>> +        page_pool_free(xa->page_pool);
>>> +
>>
>> What would you recommend to do for the following situation:
>>
>> Same receive queue is shared between 2 network devices. The receive ring is
>> filled by pages from page_pool, but you don't know the actual port (ndev)
>> filling this ring, because a device is recognized only after packet is
>> received.
>>
>> The API is so that xdp rxq is bind to network device, each frame has
>> reference
>> on it, so rxq ndev must be static. That means each netdev has it's own rxq
>> instance even no need in it. Thus, after your changes, page must be
>> returned to
>> the pool it was taken from, or released from old pool and recycled in
>> new one
>> somehow.
>>
>> And that is inconvenience at least. It's hard to move pages between
>> pools w/o
>> performance penalty. No way to use common pool either, as unreg_rxq now
>> drops
>> the pool and 2 rxqa can't reference same pool.
>>
>
>Within the single netdev, separate page_pool instances are anyway
>created for different RX rings, working under different NAPI's.

The circumstances are so that same RX ring is shared between 2
netdevs... and netdev can be known only after descriptor/packet is
received. Thus, while filling RX ring, there is no actual device,
but when packet is received it has to be recycled to appropriate
net device pool. Before this change there were no difference from
which pool the page was allocated to fill RX ring, as there were no
owner. After this change there is owner - netdev page pool.

For cpsw the dma unmap is common for both netdevs and no difference
who is freeing the page, but there is difference which pool it's
freed to.

So that, while filling RX ring the page is taken from page pool of
ndev1, but packet is received for ndev2, it has to be later
returned/recycled to page pool of ndev1, but when xdp buffer is
handed over to xdp prog the xdp_rxq_info has reference on ndev2 ...

And no way to predict the final ndev before packet is received, so no
way to choose appropriate page pool as now it becomes page owner.

So, while RX ring filling, the page/dma recycling is needed but should
be some way to identify page owner only after receiving packet.

Roughly speaking, something like:

pool->pages_state_hold_cnt++;

outside of page allocation API, after packet is received.
and free of the counter while allocation (w/o owing the page).

-- 
Regards,
Ivan Khoronzhuk

Re: [PATCH net-next v1 08/11] xdp: tracking page_pool resources and safe removal

[Ilias Apalodimas]

Hi Ivan, Tariq,

> >>>+
[...]
> >>
> >>What would you recommend to do for the following situation:
> >>
> >>Same receive queue is shared between 2 network devices. The receive ring is
> >>filled by pages from page_pool, but you don't know the actual port (ndev)
> >>filling this ring, because a device is recognized only after packet is
> >>received.
> >>
> >>The API is so that xdp rxq is bind to network device, each frame has
> >>reference
> >>on it, so rxq ndev must be static. That means each netdev has it's own rxq
> >>instance even no need in it. Thus, after your changes, page must be
> >>returned to
> >>the pool it was taken from, or released from old pool and recycled in
> >>new one
> >>somehow.
> >>
> >>And that is inconvenience at least. It's hard to move pages between
> >>pools w/o
> >>performance penalty. No way to use common pool either, as unreg_rxq now
> >>drops
> >>the pool and 2 rxqa can't reference same pool.
> >>
> >
> >Within the single netdev, separate page_pool instances are anyway
> >created for different RX rings, working under different NAPI's.
> 
> The circumstances are so that same RX ring is shared between 2
> netdevs... and netdev can be known only after descriptor/packet is
> received. Thus, while filling RX ring, there is no actual device,
> but when packet is received it has to be recycled to appropriate
> net device pool. Before this change there were no difference from
> which pool the page was allocated to fill RX ring, as there were no
> owner. After this change there is owner - netdev page pool.
> 
> For cpsw the dma unmap is common for both netdevs and no difference
> who is freeing the page, but there is difference which pool it's
> freed to.
Since 2 netdevs are sharing one queue you'll need locking right?
(Assuming that the rx-irq per device can end up on a different core)
We discussed that ideally page pools should be alocated per hardware queue. 
If you indeed need locking (and pay the performance penalty anyway) i wonder if
there's anything preventing you from keeping the same principle, i.e allocate a
pool per queue and handle the recycling to the proper ndev internally.
That way only the first device will be responsible of
allocating/recycling/maintaining the pool state.

> 
> So that, while filling RX ring the page is taken from page pool of
> ndev1, but packet is received for ndev2, it has to be later
> returned/recycled to page pool of ndev1, but when xdp buffer is
> handed over to xdp prog the xdp_rxq_info has reference on ndev2 ...
> 
> And no way to predict the final ndev before packet is received, so no
> way to choose appropriate page pool as now it becomes page owner.
> 
> So, while RX ring filling, the page/dma recycling is needed but should
> be some way to identify page owner only after receiving packet.
> 
> Roughly speaking, something like:
> 
> pool->pages_state_hold_cnt++;
> 
> outside of page allocation API, after packet is received.
> and free of the counter while allocation (w/o owing the page).
If handling it internally is not an option maybe we can sort something out for
special devices


Thanks
/Ilias

Re: [PATCH net-next v1 08/11] xdp: tracking page_pool resources and safe removal

[Ivan Khoronzhuk]

On Tue, Jun 18, 2019 at 04:30:12PM +0300, Ilias Apalodimas wrote:
>Hi Ivan, Tariq,
>
>> >>>+
>[...]
>> >>
>> >>What would you recommend to do for the following situation:
>> >>
>> >>Same receive queue is shared between 2 network devices. The receive ring is
>> >>filled by pages from page_pool, but you don't know the actual port (ndev)
>> >>filling this ring, because a device is recognized only after packet is
>> >>received.
>> >>
>> >>The API is so that xdp rxq is bind to network device, each frame has
>> >>reference
>> >>on it, so rxq ndev must be static. That means each netdev has it's own rxq
>> >>instance even no need in it. Thus, after your changes, page must be
>> >>returned to
>> >>the pool it was taken from, or released from old pool and recycled in
>> >>new one
>> >>somehow.
>> >>
>> >>And that is inconvenience at least. It's hard to move pages between
>> >>pools w/o
>> >>performance penalty. No way to use common pool either, as unreg_rxq now
>> >>drops
>> >>the pool and 2 rxqa can't reference same pool.
>> >>
>> >
>> >Within the single netdev, separate page_pool instances are anyway
>> >created for different RX rings, working under different NAPI's.
>>
>> The circumstances are so that same RX ring is shared between 2
>> netdevs... and netdev can be known only after descriptor/packet is
>> received. Thus, while filling RX ring, there is no actual device,
>> but when packet is received it has to be recycled to appropriate
>> net device pool. Before this change there were no difference from
>> which pool the page was allocated to fill RX ring, as there were no
>> owner. After this change there is owner - netdev page pool.
>>
>> For cpsw the dma unmap is common for both netdevs and no difference
>> who is freeing the page, but there is difference which pool it's
>> freed to.
>Since 2 netdevs are sharing one queue you'll need locking right?
>(Assuming that the rx-irq per device can end up on a different core)
No, rx-irq is not per device, same queue is shared only for descs,
farther it's separate queue with separate pool. Even rx-irq is per
device, no issues, as I said, it has it's own page pool, every queue
and every ndev, no need in locking, for pools...

>We discussed that ideally page pools should be alocated per hardware queue.
This is about one hw queue shared between ndevs. Page pool is separate
for each hw queues and each ndevs ofc.

>If you indeed need locking (and pay the performance penalty anyway) i wonder if
>there's anything preventing you from keeping the same principle, i.e allocate a
>pool per queue
page pool is per queue.

>pool per queue and handle the recycling to the proper ndev internally.
>That way only the first device will be responsible of
>allocating/recycling/maintaining the pool state.
No. There is more dependencies then it looks like, see rxq_info ...
The final recycling is ended not internally.

-- 
Regards,
Ivan Khoronzhuk

Re: [PATCH net-next v1 08/11] xdp: tracking page_pool resources and safe removal

[Jesper Dangaard Brouer]

On Tue, 18 Jun 2019 15:54:33 +0300 Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org> wrote:

> On Sun, Jun 16, 2019 at 10:56:25AM +0000, Tariq Toukan wrote:
> >
> >On 6/15/2019 12:33 PM, Ivan Khoronzhuk wrote:  
> >> On Thu, Jun 13, 2019 at 08:28:42PM +0200, Jesper Dangaard Brouer wrote:
[...]
> >>
> >> What would you recommend to do for the following situation:
> >>
> >> Same receive queue is shared between 2 network devices. The receive ring is
> >> filled by pages from page_pool, but you don't know the actual port (ndev)
> >> filling this ring, because a device is recognized only after packet is
> >> received.
> >>
> >> The API is so that xdp rxq is bind to network device, each frame has
> >> reference
> >> on it, so rxq ndev must be static. That means each netdev has it's own rxq
> >> instance even no need in it. Thus, after your changes, page must be
> >> returned to
> >> the pool it was taken from, or released from old pool and recycled in
> >> new one
> >> somehow.
> >>
> >> And that is inconvenience at least. It's hard to move pages between
> >> pools w/o performance penalty. No way to use common pool either,
> >> as unreg_rxq now drops the pool and 2 rxqa can't reference same
> >> pool. 
> >
> >Within the single netdev, separate page_pool instances are anyway
> >created for different RX rings, working under different NAPI's.  
> 
> The circumstances are so that same RX ring is shared between 2
> netdevs... and netdev can be known only after descriptor/packet is
> received. Thus, while filling RX ring, there is no actual device,
> but when packet is received it has to be recycled to appropriate
> net device pool. Before this change there were no difference from
> which pool the page was allocated to fill RX ring, as there were no
> owner. After this change there is owner - netdev page pool.

It not really a dependency added in this patchset.  A page_pool is
strictly bound to a single RX-queue, for performance, as this allow us
a NAPI fast-path return used for early drop (XDP_DROP).

I can see that the API xdp_rxq_info_reg_mem_model() make it possible to
call it on different xdp_rxq_info structs with the same page_pool
pointer.  But it was never intended to be used like that, and I
consider it an API usage violation.  I originally wanted to add the
allocator pointer to xdp_rxq_info_reg() call, but the API was extended
in different versions, so I didn't want to break users.  I've actually
tried hard to catch when drivers use the API wrong, via WARN(), but I
guess you found a loop hole.

Besides, we already have a dependency from the RX-queue to the netdev
in the xdp_rxq_info structure.  E.g. the xdp_rxq_info->dev is sort of
central, and dereferenced by BPF-code to read xdp_md->ingress_ifindex,
and also used by cpumap when creating SKBs.


> For cpsw the dma unmap is common for both netdevs and no difference
> who is freeing the page, but there is difference which pool it's
> freed to.
> 
> So that, while filling RX ring the page is taken from page pool of
> ndev1, but packet is received for ndev2, it has to be later
> returned/recycled to page pool of ndev1, but when xdp buffer is
> handed over to xdp prog the xdp_rxq_info has reference on ndev2 ...
>
> And no way to predict the final ndev before packet is received, so no
> way to choose appropriate page pool as now it becomes page owner.
> 
> So, while RX ring filling, the page/dma recycling is needed but should
> be some way to identify page owner only after receiving packet.
> 
> Roughly speaking, something like:
> 
> pool->pages_state_hold_cnt++;
> 
> outside of page allocation API, after packet is received.

Don't EVER manipulate the internal state outside of page allocation
API.  That kills the purpose of defining any API.

> and free of the counter while allocation (w/o owing the page).

You use-case of two netdev's sharing the same RX-queue sounds dubious,
and very hardware specific.  I'm not sure why we want to bend the APIs
to support this?
 If we had to allow page_pool to be registered twice, via
xdp_rxq_info_reg_mem_model() then I guess we could extend page_pool
with a usage/users reference count, and then only really free the
page_pool when refcnt reach zero.  But it just seems and looks wrong
(in the code) as the hole trick to get performance is to only have one
user.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer

Re: [PATCH net-next v1 08/11] xdp: tracking page_pool resources and safe removal

[Ivan Khoronzhuk]

On Tue, Jun 18, 2019 at 05:19:51PM +0200, Jesper Dangaard Brouer wrote:
Hi, Jesper

>
>On Tue, 18 Jun 2019 15:54:33 +0300 Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org> wrote:
>
>> On Sun, Jun 16, 2019 at 10:56:25AM +0000, Tariq Toukan wrote:
>> >
>> >On 6/15/2019 12:33 PM, Ivan Khoronzhuk wrote:
>> >> On Thu, Jun 13, 2019 at 08:28:42PM +0200, Jesper Dangaard Brouer wrote:
>[...]
>> >>
>> >> What would you recommend to do for the following situation:
>> >>
>> >> Same receive queue is shared between 2 network devices. The receive ring is
>> >> filled by pages from page_pool, but you don't know the actual port (ndev)
>> >> filling this ring, because a device is recognized only after packet is
>> >> received.
>> >>
>> >> The API is so that xdp rxq is bind to network device, each frame has
>> >> reference
>> >> on it, so rxq ndev must be static. That means each netdev has it's own rxq
>> >> instance even no need in it. Thus, after your changes, page must be
>> >> returned to
>> >> the pool it was taken from, or released from old pool and recycled in
>> >> new one
>> >> somehow.
>> >>
>> >> And that is inconvenience at least. It's hard to move pages between
>> >> pools w/o performance penalty. No way to use common pool either,
>> >> as unreg_rxq now drops the pool and 2 rxqa can't reference same
>> >> pool.
>> >
>> >Within the single netdev, separate page_pool instances are anyway
>> >created for different RX rings, working under different NAPI's.
>>
>> The circumstances are so that same RX ring is shared between 2
>> netdevs... and netdev can be known only after descriptor/packet is
>> received. Thus, while filling RX ring, there is no actual device,
>> but when packet is received it has to be recycled to appropriate
>> net device pool. Before this change there were no difference from
>> which pool the page was allocated to fill RX ring, as there were no
>> owner. After this change there is owner - netdev page pool.
>
>It not really a dependency added in this patchset.  A page_pool is
>strictly bound to a single RX-queue, for performance, as this allow us
>a NAPI fast-path return used for early drop (XDP_DROP).
>
>I can see that the API xdp_rxq_info_reg_mem_model() make it possible to
>call it on different xdp_rxq_info structs with the same page_pool
>pointer.  But it was never intended to be used like that, and I
>consider it an API usage violation.  I originally wanted to add the
>allocator pointer to xdp_rxq_info_reg() call, but the API was extended
>in different versions, so I didn't want to break users.  I've actually
>tried hard to catch when drivers use the API wrong, via WARN(), but I
>guess you found a loop hole.
>
>Besides, we already have a dependency from the RX-queue to the netdev
>in the xdp_rxq_info structure.
>E.g. the xdp_rxq_info->dev is sort of
>central, and dereferenced by BPF-code to read xdp_md->ingress_ifindex,
>and also used by cpumap when creating SKBs.
Yes, That's I'm talking about.

>
>
>> For cpsw the dma unmap is common for both netdevs and no difference
>> who is freeing the page, but there is difference which pool it's
>> freed to.
>>
>> So that, while filling RX ring the page is taken from page pool of
>> ndev1, but packet is received for ndev2, it has to be later
>> returned/recycled to page pool of ndev1, but when xdp buffer is
>> handed over to xdp prog the xdp_rxq_info has reference on ndev2 ...
>>
>> And no way to predict the final ndev before packet is received, so no
>> way to choose appropriate page pool as now it becomes page owner.
>>
>> So, while RX ring filling, the page/dma recycling is needed but should
>> be some way to identify page owner only after receiving packet.
>>
>> Roughly speaking, something like:
>>
>> pool->pages_state_hold_cnt++;
>>
>> outside of page allocation API, after packet is received.
>
>Don't EVER manipulate the internal state outside of page allocation
>API.  That kills the purpose of defining any API.
And I don't, that's rough propose that can be covered by newer API and here kind
of material for explanation.

This RX ring is filled by internal descriptors for 2 netdevs, it's common only
internally. But to bind descriptor with a page, the page must be allocated from
pool bind to ndev, In case of cpsw, ndev is identified only after the
descriptor/packet is received. Then, it can be related to some ndev and thus
pool. The example in question only shows what API needs to allow underneath.

For this, the following is needed:

1) Allocate page from page pool, but w/o counter inc, so driver can became the
owner and bind it with a descriptor and put it to RX ring for receiving a
packet by h/w.

2) after a packet is received the counter needs to be inc for a pool the packet
is destined for and let xdp infrastructure do the rest.

That's it.
I don't propose to change the API for those who doesn't require it,
just let to use more detailed variant for those who can't use it in regular way.

And it's not final decision would be nice to hear another constructive
propositions.

>
>> and free of the counter while allocation (w/o owing the page).
>
>You use-case of two netdev's sharing the same RX-queue sounds dubious,
>and very hardware specific.  I'm not sure why we want to bend the APIs
>to support this?
The question is rather why not? The allocator is supposed to be used as one of
the main generic solutions for XDP, if not say more, it should be able to cover
most of the hardware, not only for hi speed solutions, but for other usecases.
I don't propose to change main API, left it as is, just extend it that not only
single ndev hardware can use it... I can add it myself if you don't want to
bother.

> If we had to allow page_pool to be registered twice, via
>xdp_rxq_info_reg_mem_model() then I guess we could extend page_pool
>with a usage/users reference count, and then only really free the
>page_pool when refcnt reach zero.  But it just seems and looks wrong
>(in the code) as the hole trick to get performance is to only have one
>user.
I don't propose this.

>
>-- 
>Best regards,
>  Jesper Dangaard Brouer
>  MSc.CS, Principal Kernel Engineer at Red Hat
>  LinkedIn: http://www.linkedin.com/in/brouer

-- 
Regards,
Ivan Khoronzhuk

Re: [PATCH net-next v1 08/11] xdp: tracking page_pool resources and safe removal

[Ivan Khoronzhuk]

On Tue, Jun 18, 2019 at 08:54:07PM +0300, Ivan Khoronzhuk wrote:
Hi, Jesper

>On Tue, Jun 18, 2019 at 05:19:51PM +0200, Jesper Dangaard Brouer wrote:
>

[...]

>>If we had to allow page_pool to be registered twice, via
>>xdp_rxq_info_reg_mem_model() then I guess we could extend page_pool
>>with a usage/users reference count, and then only really free the
>>page_pool when refcnt reach zero.  But it just seems and looks wrong
>>(in the code) as the hole trick to get performance is to only have one
>>user.

Let's try this variant. This might be used only in case if no choice.
If no issues and provide appropriate comments in the code it can look
more a while normal.

-- 
Regards,
Ivan Khoronzhuk

[PATCH net-next v1 09/11] xdp: force mem allocator removal and periodic warning

[Jesper Dangaard Brouer]

If bugs exists or are introduced later e.g. by drivers misusing the API,
then we want to warn about the issue, such that developer notice. This patch
will generate a bit of noise in form of periodic pr_warn every 30 seconds.

It is not nice to have this stall warning running forever. Thus, this patch
will (after 120 attempts) force disconnect the mem id (from the rhashtable)
and free the page_pool object. This will cause fallback to the put_page() as
before, which only potentially leak DMA-mappings, if objects are really
stuck for this long. In that unlikely case, a WARN_ONCE should show us the
call stack.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
---
 net/core/page_pool.c |   18 +++++++++++++++++-
 net/core/xdp.c       |   37 +++++++++++++++++++++++++++++++------
 2 files changed, 48 insertions(+), 7 deletions(-)

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 8679e24fd665..42c3b0a5a259 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -330,11 +330,27 @@ static void __page_pool_empty_ring(struct page_pool *pool)
 	}
 }
 
+static void __warn_in_flight(struct page_pool *pool)
+{
+	u32 release_cnt = atomic_read(&pool->pages_state_release_cnt);
+	u32 hold_cnt = READ_ONCE(pool->pages_state_hold_cnt);
+	s32 distance;
+
+	distance = _distance(hold_cnt, release_cnt);
+
+	/* Drivers should fix this, but only problematic when DMA is used */
+	WARN(1, "Still in-flight pages:%d hold:%u released:%u",
+	     distance, hold_cnt, release_cnt);
+}
+
 void __page_pool_free(struct page_pool *pool)
 {
 	WARN(pool->alloc.count, "API usage violation");
 	WARN(!ptr_ring_empty(&pool->ring), "ptr_ring is not empty");
-	WARN(!__page_pool_safe_to_destroy(pool), "still in-flight pages");
+
+	/* Can happen due to forced shutdown */
+	if (!__page_pool_safe_to_destroy(pool))
+		__warn_in_flight(pool);
 
 	ptr_ring_cleanup(&pool->ring, NULL);
 	kfree(pool);
diff --git a/net/core/xdp.c b/net/core/xdp.c
index 2b7bad227030..53bce4fa776a 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -39,6 +39,9 @@ struct xdp_mem_allocator {
 	struct rhash_head node;
 	struct rcu_head rcu;
 	struct delayed_work defer_wq;
+	unsigned long defer_start;
+	unsigned long defer_warn;
+	int disconnect_cnt;
 };
 
 static u32 xdp_mem_id_hashfn(const void *data, u32 len, u32 seed)
@@ -95,7 +98,7 @@ static void __xdp_mem_allocator_rcu_free(struct rcu_head *rcu)
 	kfree(xa);
 }
 
-bool __mem_id_disconnect(int id)
+bool __mem_id_disconnect(int id, bool force)
 {
 	struct xdp_mem_allocator *xa;
 	bool safe_to_remove = true;
@@ -108,29 +111,47 @@ bool __mem_id_disconnect(int id)
 		WARN(1, "Request remove non-existing id(%d), driver bug?", id);
 		return true;
 	}
+	xa->disconnect_cnt++;
 
 	/* Detects in-flight packet-pages for page_pool */
 	if (xa->mem.type == MEM_TYPE_PAGE_POOL)
 		safe_to_remove = page_pool_request_shutdown(xa->page_pool);
 
-	if (safe_to_remove &&
+	/* TODO: Tracepoint will be added here in next-patch */
+
+	if ((safe_to_remove || force) &&
 	    !rhashtable_remove_fast(mem_id_ht, &xa->node, mem_id_rht_params))
 		call_rcu(&xa->rcu, __xdp_mem_allocator_rcu_free);
 
 	mutex_unlock(&mem_id_lock);
-	return safe_to_remove;
+	return (safe_to_remove|force);
 }
 
 #define DEFER_TIME (msecs_to_jiffies(1000))
+#define DEFER_WARN_INTERVAL (30 * HZ)
+#define DEFER_MAX_RETRIES 120
 
 static void mem_id_disconnect_defer_retry(struct work_struct *wq)
 {
 	struct delayed_work *dwq = to_delayed_work(wq);
 	struct xdp_mem_allocator *xa = container_of(dwq, typeof(*xa), defer_wq);
+	bool force = false;
+
+	if (xa->disconnect_cnt > DEFER_MAX_RETRIES)
+		force = true;
 
-	if (__mem_id_disconnect(xa->mem.id))
+	if (__mem_id_disconnect(xa->mem.id, force))
 		return;
 
+	/* Periodic warning */
+	if (time_after_eq(jiffies, xa->defer_warn)) {
+		int sec = (s32)((u32)jiffies - (u32)xa->defer_start) / HZ;
+
+		pr_warn("%s() stalled mem.id=%u shutdown %d attempts %d sec\n",
+			__func__, xa->mem.id, xa->disconnect_cnt, sec);
+		xa->defer_warn = jiffies + DEFER_WARN_INTERVAL;
+	}
+
 	/* Still not ready to be disconnected, retry later */
 	schedule_delayed_work(&xa->defer_wq, DEFER_TIME);
 }
@@ -153,7 +174,7 @@ void xdp_rxq_info_unreg_mem_model(struct xdp_rxq_info *xdp_rxq)
 	if (id == 0)
 		return;
 
-	if (__mem_id_disconnect(id))
+	if (__mem_id_disconnect(id, false))
 		return;
 
 	/* Could not disconnect, defer new disconnect attempt to later */
@@ -164,6 +185,8 @@ void xdp_rxq_info_unreg_mem_model(struct xdp_rxq_info *xdp_rxq)
 		mutex_unlock(&mem_id_lock);
 		return;
 	}
+	xa->defer_start = jiffies;
+	xa->defer_warn  = jiffies + DEFER_WARN_INTERVAL;
 
 	INIT_DELAYED_WORK(&xa->defer_wq, mem_id_disconnect_defer_retry);
 	mutex_unlock(&mem_id_lock);
@@ -388,10 +411,12 @@ static void __xdp_return(void *data, struct xdp_mem_info *mem, bool napi_direct,
 		/* mem->id is valid, checked in xdp_rxq_info_reg_mem_model() */
 		xa = rhashtable_lookup(mem_id_ht, &mem->id, mem_id_rht_params);
 		page = virt_to_head_page(data);
-		if (xa) {
+		if (likely(xa)) {
 			napi_direct &= !xdp_return_frame_no_direct();
 			page_pool_put_page(xa->page_pool, page, napi_direct);
 		} else {
+			/* Hopefully stack show who to blame for late return */
+			WARN_ONCE(1, "page_pool gone mem.id=%d", mem->id);
 			put_page(page);
 		}
 		rcu_read_unlock();

Re: [PATCH net-next v1 09/11] xdp: force mem allocator removal and periodic warning

[Ivan Khoronzhuk]

On Thu, Jun 13, 2019 at 08:28:47PM +0200, Jesper Dangaard Brouer wrote:
>If bugs exists or are introduced later e.g. by drivers misusing the API,
>then we want to warn about the issue, such that developer notice. This patch
>will generate a bit of noise in form of periodic pr_warn every 30 seconds.
>
>It is not nice to have this stall warning running forever. Thus, this patch
>will (after 120 attempts) force disconnect the mem id (from the rhashtable)
>and free the page_pool object. This will cause fallback to the put_page() as
>before, which only potentially leak DMA-mappings, if objects are really
>stuck for this long. In that unlikely case, a WARN_ONCE should show us the
>call stack.
>
>Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
>---
> net/core/page_pool.c |   18 +++++++++++++++++-
> net/core/xdp.c       |   37 +++++++++++++++++++++++++++++++------
> 2 files changed, 48 insertions(+), 7 deletions(-)
>
>diff --git a/net/core/page_pool.c b/net/core/page_pool.c
>index 8679e24fd665..42c3b0a5a259 100644
>--- a/net/core/page_pool.c
>+++ b/net/core/page_pool.c
>@@ -330,11 +330,27 @@ static void __page_pool_empty_ring(struct page_pool *pool)
> 	}
> }
>
>+static void __warn_in_flight(struct page_pool *pool)
>+{
>+	u32 release_cnt = atomic_read(&pool->pages_state_release_cnt);
>+	u32 hold_cnt = READ_ONCE(pool->pages_state_hold_cnt);
>+	s32 distance;
>+
>+	distance = _distance(hold_cnt, release_cnt);
>+
>+	/* Drivers should fix this, but only problematic when DMA is used */
>+	WARN(1, "Still in-flight pages:%d hold:%u released:%u",
>+	     distance, hold_cnt, release_cnt);
>+}
>+
> void __page_pool_free(struct page_pool *pool)
> {
> 	WARN(pool->alloc.count, "API usage violation");
> 	WARN(!ptr_ring_empty(&pool->ring), "ptr_ring is not empty");
>-	WARN(!__page_pool_safe_to_destroy(pool), "still in-flight pages");
>+
>+	/* Can happen due to forced shutdown */
>+	if (!__page_pool_safe_to_destroy(pool))
>+		__warn_in_flight(pool);
>
> 	ptr_ring_cleanup(&pool->ring, NULL);
> 	kfree(pool);
>diff --git a/net/core/xdp.c b/net/core/xdp.c
>index 2b7bad227030..53bce4fa776a 100644
>--- a/net/core/xdp.c
>+++ b/net/core/xdp.c
>@@ -39,6 +39,9 @@ struct xdp_mem_allocator {
> 	struct rhash_head node;
> 	struct rcu_head rcu;
> 	struct delayed_work defer_wq;
>+	unsigned long defer_start;
>+	unsigned long defer_warn;
>+	int disconnect_cnt;
> };
>
> static u32 xdp_mem_id_hashfn(const void *data, u32 len, u32 seed)
>@@ -95,7 +98,7 @@ static void __xdp_mem_allocator_rcu_free(struct rcu_head *rcu)
> 	kfree(xa);
> }
>
>-bool __mem_id_disconnect(int id)
>+bool __mem_id_disconnect(int id, bool force)
> {
> 	struct xdp_mem_allocator *xa;
> 	bool safe_to_remove = true;
>@@ -108,29 +111,47 @@ bool __mem_id_disconnect(int id)
> 		WARN(1, "Request remove non-existing id(%d), driver bug?", id);
> 		return true;
> 	}
>+	xa->disconnect_cnt++;
>
> 	/* Detects in-flight packet-pages for page_pool */
> 	if (xa->mem.type == MEM_TYPE_PAGE_POOL)
> 		safe_to_remove = page_pool_request_shutdown(xa->page_pool);
>
>-	if (safe_to_remove &&
>+	/* TODO: Tracepoint will be added here in next-patch */
>+
>+	if ((safe_to_remove || force) &&
> 	    !rhashtable_remove_fast(mem_id_ht, &xa->node, mem_id_rht_params))
> 		call_rcu(&xa->rcu, __xdp_mem_allocator_rcu_free);
>
> 	mutex_unlock(&mem_id_lock);
>-	return safe_to_remove;
>+	return (safe_to_remove|force);
> }
>
> #define DEFER_TIME (msecs_to_jiffies(1000))
>+#define DEFER_WARN_INTERVAL (30 * HZ)
>+#define DEFER_MAX_RETRIES 120
>
> static void mem_id_disconnect_defer_retry(struct work_struct *wq)
> {
> 	struct delayed_work *dwq = to_delayed_work(wq);
> 	struct xdp_mem_allocator *xa = container_of(dwq, typeof(*xa), defer_wq);
>+	bool force = false;
>+
>+	if (xa->disconnect_cnt > DEFER_MAX_RETRIES)
>+		force = true;
>
>-	if (__mem_id_disconnect(xa->mem.id))
>+	if (__mem_id_disconnect(xa->mem.id, force))
> 		return;
>
>+	/* Periodic warning */
>+	if (time_after_eq(jiffies, xa->defer_warn)) {
>+		int sec = (s32)((u32)jiffies - (u32)xa->defer_start) / HZ;
>+
>+		pr_warn("%s() stalled mem.id=%u shutdown %d attempts %d sec\n",
>+			__func__, xa->mem.id, xa->disconnect_cnt, sec);
>+		xa->defer_warn = jiffies + DEFER_WARN_INTERVAL;
>+	}
>+
> 	/* Still not ready to be disconnected, retry later */
> 	schedule_delayed_work(&xa->defer_wq, DEFER_TIME);
> }
>@@ -153,7 +174,7 @@ void xdp_rxq_info_unreg_mem_model(struct xdp_rxq_info *xdp_rxq)
> 	if (id == 0)
> 		return;
>
>-	if (__mem_id_disconnect(id))
>+	if (__mem_id_disconnect(id, false))
> 		return;
>
> 	/* Could not disconnect, defer new disconnect attempt to later */
>@@ -164,6 +185,8 @@ void xdp_rxq_info_unreg_mem_model(struct xdp_rxq_info *xdp_rxq)
> 		mutex_unlock(&mem_id_lock);
> 		return;
> 	}
>+	xa->defer_start = jiffies;
>+	xa->defer_warn  = jiffies + DEFER_WARN_INTERVAL;
>
> 	INIT_DELAYED_WORK(&xa->defer_wq, mem_id_disconnect_defer_retry);
> 	mutex_unlock(&mem_id_lock);
>@@ -388,10 +411,12 @@ static void __xdp_return(void *data, struct xdp_mem_info *mem, bool napi_direct,
> 		/* mem->id is valid, checked in xdp_rxq_info_reg_mem_model() */
> 		xa = rhashtable_lookup(mem_id_ht, &mem->id, mem_id_rht_params);
> 		page = virt_to_head_page(data);
>-		if (xa) {
>+		if (likely(xa)) {
> 			napi_direct &= !xdp_return_frame_no_direct();
> 			page_pool_put_page(xa->page_pool, page, napi_direct);
Interesting if it's synced with device "unregistration".
I mean page dma unmap is bind to device that doesn't exist anymore but pages
from pool of the device are in flight, so pool is not destroyed but what about
device?. smth like device unreq todo list. Just to be sure, is it synched?

> 		} else {
>+			/* Hopefully stack show who to blame for late return */
>+			WARN_ONCE(1, "page_pool gone mem.id=%d", mem->id);
> 			put_page(page);
> 		}
> 		rcu_read_unlock();
>

-- 
Regards,
Ivan Khoronzhuk

Re: [PATCH net-next v1 09/11] xdp: force mem allocator removal and periodic warning

[Jesper Dangaard Brouer]

On Sat, 15 Jun 2019 11:59:16 +0300
Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org> wrote:

> >@@ -388,10 +411,12 @@ static void __xdp_return(void *data, struct xdp_mem_info *mem, bool napi_direct,
> > 		/* mem->id is valid, checked in xdp_rxq_info_reg_mem_model() */
> > 		xa = rhashtable_lookup(mem_id_ht, &mem->id, mem_id_rht_params);
> > 		page = virt_to_head_page(data);
> >-		if (xa) {
> >+		if (likely(xa)) {
> > 			napi_direct &= !xdp_return_frame_no_direct();
> > 			page_pool_put_page(xa->page_pool, page, napi_direct);
>
> Interesting if it's synced with device "unregistration".
> I mean page dma unmap is bind to device that doesn't exist anymore but pages
> from pool of the device are in flight, so pool is not destroyed but what about
> device?. smth like device unreq todo list. Just to be sure, is it synched?

I looked through the code, and you are right.  We are actually missing
to hold a reference count on struct device (for which we use dev->dma_ops).
It looks like we can simply do a get_device() and put_device(). Thus,
fairly simple to fix.

I'll add this fix as a separate patch, as it is a separate issue/bug
that also needs correction... Thanks for catching this!

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer

[PATCH net-next v1 10/11] xdp: add tracepoints for XDP mem

[Jesper Dangaard Brouer]

These tracepoints make it easier to troubleshoot XDP mem id disconnect.

The xdp:mem_disconnect tracepoint cannot be replaced via kprobe. It is
placed at the last stable place for the pointer to struct xdp_mem_allocator,
just before it's scheduled for RCU removal. It also extract info on
'safe_to_remove' and 'force'.

Detailed info about in-flight pages is not available at this layer. The next
patch will added tracepoints needed at the page_pool layer for this.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
---
 include/net/xdp_priv.h     |   23 +++++++++
 include/trace/events/xdp.h |  115 ++++++++++++++++++++++++++++++++++++++++++++
 net/core/xdp.c             |   21 ++------
 3 files changed, 143 insertions(+), 16 deletions(-)
 create mode 100644 include/net/xdp_priv.h

diff --git a/include/net/xdp_priv.h b/include/net/xdp_priv.h
new file mode 100644
index 000000000000..6a8cba6ea79a
--- /dev/null
+++ b/include/net/xdp_priv.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __LINUX_NET_XDP_PRIV_H__
+#define __LINUX_NET_XDP_PRIV_H__
+
+#include <linux/rhashtable.h>
+
+/* Private to net/core/xdp.c, but used by trace/events/xdp.h */
+struct xdp_mem_allocator {
+	struct xdp_mem_info mem;
+	union {
+		void *allocator;
+		struct page_pool *page_pool;
+		struct zero_copy_allocator *zc_alloc;
+	};
+	int disconnect_cnt;
+	unsigned long defer_start;
+	struct rhash_head node;
+	struct rcu_head rcu;
+	struct delayed_work defer_wq;
+	unsigned long defer_warn;
+};
+
+#endif /* __LINUX_NET_XDP_PRIV_H__ */
diff --git a/include/trace/events/xdp.h b/include/trace/events/xdp.h
index e95cb86b65cf..bb5e380e2ef3 100644
--- a/include/trace/events/xdp.h
+++ b/include/trace/events/xdp.h
@@ -269,6 +269,121 @@ TRACE_EVENT(xdp_devmap_xmit,
 		  __entry->from_ifindex, __entry->to_ifindex, __entry->err)
 );
 
+/* Expect users already include <net/xdp.h>, but not xdp_priv.h */
+#include <net/xdp_priv.h>
+
+#define __MEM_TYPE_MAP(FN)	\
+	FN(PAGE_SHARED)		\
+	FN(PAGE_ORDER0)		\
+	FN(PAGE_POOL)		\
+	FN(ZERO_COPY)
+
+#define __MEM_TYPE_TP_FN(x)	\
+	TRACE_DEFINE_ENUM(MEM_TYPE_##x);
+#define __MEM_TYPE_SYM_FN(x)	\
+	{ MEM_TYPE_##x, #x },
+#define __MEM_TYPE_SYM_TAB	\
+	__MEM_TYPE_MAP(__MEM_TYPE_SYM_FN) { -1, 0 }
+__MEM_TYPE_MAP(__MEM_TYPE_TP_FN)
+
+TRACE_EVENT(mem_disconnect,
+
+	TP_PROTO(const struct xdp_mem_allocator *xa,
+		 bool safe_to_remove, bool force),
+
+	TP_ARGS(xa, safe_to_remove, force),
+
+	TP_STRUCT__entry(
+		__field(const struct xdp_mem_allocator *,	xa)
+		__field(u32,		mem_id)
+		__field(u32,		mem_type)
+		__field(const void *,	allocator)
+		__field(bool,		safe_to_remove)
+		__field(bool,		force)
+		__field(int,		disconnect_cnt)
+	),
+
+	TP_fast_assign(
+		__entry->xa		= xa;
+		__entry->mem_id		= xa->mem.id;
+		__entry->mem_type	= xa->mem.type;
+		__entry->allocator	= xa->allocator;
+		__entry->safe_to_remove	= safe_to_remove;
+		__entry->force		= force;
+		__entry->disconnect_cnt	= xa->disconnect_cnt;
+	),
+
+	TP_printk("mem_id=%d mem_type=%s allocator=%p"
+		  " safe_to_remove=%s force=%s disconnect_cnt=%d",
+		  __entry->mem_id,
+		  __print_symbolic(__entry->mem_type, __MEM_TYPE_SYM_TAB),
+		  __entry->allocator,
+		  __entry->safe_to_remove ? "true" : "false",
+		  __entry->force ? "true" : "false",
+		  __entry->disconnect_cnt
+	)
+);
+
+TRACE_EVENT(mem_connect,
+
+	TP_PROTO(const struct xdp_mem_allocator *xa,
+		 const struct xdp_rxq_info *rxq),
+
+	TP_ARGS(xa, rxq),
+
+	TP_STRUCT__entry(
+		__field(const struct xdp_mem_allocator *,	xa)
+		__field(u32,		mem_id)
+		__field(u32,		mem_type)
+		__field(const void *,	allocator)
+		__field(const struct xdp_rxq_info *,		rxq)
+		__field(int,		ifindex)
+	),
+
+	TP_fast_assign(
+		__entry->xa		= xa;
+		__entry->mem_id		= xa->mem.id;
+		__entry->mem_type	= xa->mem.type;
+		__entry->allocator	= xa->allocator;
+		__entry->rxq		= rxq;
+		__entry->ifindex	= rxq->dev->ifindex;
+	),
+
+	TP_printk("mem_id=%d mem_type=%s allocator=%p"
+		  " ifindex=%d",
+		  __entry->mem_id,
+		  __print_symbolic(__entry->mem_type, __MEM_TYPE_SYM_TAB),
+		  __entry->allocator,
+		  __entry->ifindex
+	)
+);
+
+TRACE_EVENT(mem_return_failed,
+
+	TP_PROTO(const struct xdp_mem_info *mem,
+		 const struct page *page),
+
+	TP_ARGS(mem, page),
+
+	TP_STRUCT__entry(
+		__field(const struct page *,	page)
+		__field(u32,		mem_id)
+		__field(u32,		mem_type)
+	),
+
+	TP_fast_assign(
+		__entry->page		= page;
+		__entry->mem_id		= mem->id;
+		__entry->mem_type	= mem->type;
+	),
+
+	TP_printk("mem_id=%d mem_type=%s page=%p",
+		  __entry->mem_id,
+		  __print_symbolic(__entry->mem_type, __MEM_TYPE_SYM_TAB),
+		  __entry->page
+	)
+);
+
 #endif /* _TRACE_XDP_H */
 
 #include <trace/define_trace.h>
diff --git a/net/core/xdp.c b/net/core/xdp.c
index 53bce4fa776a..4ad9e48b76a8 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -14,6 +14,8 @@
 #include <net/page_pool.h>
 
 #include <net/xdp.h>
+#include <net/xdp_priv.h> /* struct xdp_mem_allocator */
+#include <trace/events/xdp.h>
 
 #define REG_STATE_NEW		0x0
 #define REG_STATE_REGISTERED	0x1
@@ -29,21 +31,6 @@ static int mem_id_next = MEM_ID_MIN;
 static bool mem_id_init; /* false */
 static struct rhashtable *mem_id_ht;
 
-struct xdp_mem_allocator {
-	struct xdp_mem_info mem;
-	union {
-		void *allocator;
-		struct page_pool *page_pool;
-		struct zero_copy_allocator *zc_alloc;
-	};
-	struct rhash_head node;
-	struct rcu_head rcu;
-	struct delayed_work defer_wq;
-	unsigned long defer_start;
-	unsigned long defer_warn;
-	int disconnect_cnt;
-};
-
 static u32 xdp_mem_id_hashfn(const void *data, u32 len, u32 seed)
 {
 	const u32 *k = data;
@@ -117,7 +104,7 @@ bool __mem_id_disconnect(int id, bool force)
 	if (xa->mem.type == MEM_TYPE_PAGE_POOL)
 		safe_to_remove = page_pool_request_shutdown(xa->page_pool);
 
-	/* TODO: Tracepoint will be added here in next-patch */
+	trace_mem_disconnect(xa, safe_to_remove, force);
 
 	if ((safe_to_remove || force) &&
 	    !rhashtable_remove_fast(mem_id_ht, &xa->node, mem_id_rht_params))
@@ -385,6 +372,7 @@ int xdp_rxq_info_reg_mem_model(struct xdp_rxq_info *xdp_rxq,
 
 	mutex_unlock(&mem_id_lock);
 
+	trace_mem_connect(xdp_alloc, xdp_rxq);
 	return 0;
 err:
 	mutex_unlock(&mem_id_lock);
@@ -417,6 +405,7 @@ static void __xdp_return(void *data, struct xdp_mem_info *mem, bool napi_direct,
 		} else {
 			/* Hopefully stack show who to blame for late return */
 			WARN_ONCE(1, "page_pool gone mem.id=%d", mem->id);
+			trace_mem_return_failed(mem, page);
 			put_page(page);
 		}
 		rcu_read_unlock();

[PATCH net-next v1 11/11] page_pool: add tracepoints for page_pool with details need by XDP

[Jesper Dangaard Brouer]

The xdp tracepoints for mem id disconnect don't carry information about, why
it was not safe_to_remove.  The tracepoint page_pool:page_pool_inflight in
this patch can be used for extract this info for further debugging.

This patchset also adds tracepoint for the pages_state_* release/hold
transitions, including a pointer to the page.  This can be used for stats
about in-flight pages, or used to debug page leakage via keeping track of
page pointer and combining this with kprobe for __put_page().

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
---
 include/trace/events/page_pool.h |   87 ++++++++++++++++++++++++++++++++++++++
 net/core/net-traces.c            |    4 ++
 net/core/page_pool.c             |    9 +++-
 3 files changed, 99 insertions(+), 1 deletion(-)
 create mode 100644 include/trace/events/page_pool.h

diff --git a/include/trace/events/page_pool.h b/include/trace/events/page_pool.h
new file mode 100644
index 000000000000..47b5ee880aa9
--- /dev/null
+++ b/include/trace/events/page_pool.h
@@ -0,0 +1,87 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM page_pool
+
+#if !defined(_TRACE_PAGE_POOL_H) || defined(TRACE_HEADER_MULTI_READ)
+#define      _TRACE_PAGE_POOL_H
+
+#include <linux/types.h>
+#include <linux/tracepoint.h>
+
+#include <net/page_pool.h>
+
+TRACE_EVENT(page_pool_inflight,
+
+	TP_PROTO(const struct page_pool *pool,
+		 s32 inflight, u32 hold, u32 release),
+
+	TP_ARGS(pool, inflight, hold, release),
+
+	TP_STRUCT__entry(
+		__field(const struct page_pool *, pool)
+		__field(s32,	inflight)
+		__field(u32,	hold)
+		__field(u32,	release)
+	),
+
+	TP_fast_assign(
+		__entry->pool		= pool;
+		__entry->inflight	= inflight;
+		__entry->hold		= hold;
+		__entry->release	= release;
+	),
+
+	TP_printk("page_pool=%p inflight=%d hold=%u release=%u",
+	  __entry->pool, __entry->inflight, __entry->hold, __entry->release)
+);
+
+TRACE_EVENT(page_pool_state_release,
+
+	TP_PROTO(const struct page_pool *pool,
+		 const struct page *page, u32 release),
+
+	TP_ARGS(pool, page, release),
+
+	TP_STRUCT__entry(
+		__field(const struct page_pool *,	pool)
+		__field(const struct page *,		page)
+		__field(u32,				release)
+	),
+
+	TP_fast_assign(
+		__entry->pool		= pool;
+		__entry->page		= page;
+		__entry->release	= release;
+	),
+
+	TP_printk("page_pool=%p page=%p release=%u",
+		  __entry->pool, __entry->page, __entry->release)
+);
+
+TRACE_EVENT(page_pool_state_hold,
+
+	TP_PROTO(const struct page_pool *pool,
+		 const struct page *page, u32 hold),
+
+	TP_ARGS(pool, page, hold),
+
+	TP_STRUCT__entry(
+		__field(const struct page_pool *,	pool)
+		__field(const struct page *,		page)
+		__field(u32,				hold)
+	),
+
+	TP_fast_assign(
+		__entry->pool	= pool;
+		__entry->page	= page;
+		__entry->hold	= hold;
+	),
+
+	TP_printk("page_pool=%p page=%p hold=%u",
+		  __entry->pool, __entry->page, __entry->hold)
+);
+
+#endif /* _TRACE_PAGE_POOL_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/net/core/net-traces.c b/net/core/net-traces.c
index 470b179d599e..283ddb2dbc7d 100644
--- a/net/core/net-traces.c
+++ b/net/core/net-traces.c
@@ -43,6 +43,10 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(fdb_delete);
 EXPORT_TRACEPOINT_SYMBOL_GPL(br_fdb_update);
 #endif
 
+#if IS_ENABLED(CONFIG_PAGE_POOL)
+#include <trace/events/page_pool.h>
+#endif
+
 #include <trace/events/neigh.h>
 EXPORT_TRACEPOINT_SYMBOL_GPL(neigh_update);
 EXPORT_TRACEPOINT_SYMBOL_GPL(neigh_update_done);
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 42c3b0a5a259..f55ab055d543 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -4,6 +4,7 @@
  *	Author:	Jesper Dangaard Brouer <netoptimizer@brouer.com>
  *	Copyright (C) 2016 Red Hat, Inc.
  */
+
 #include <linux/types.h>
 #include <linux/kernel.h>
 #include <linux/slab.h>
@@ -14,6 +15,8 @@
 #include <linux/page-flags.h>
 #include <linux/mm.h> /* for __put_page() */
 
+#include <trace/events/page_pool.h>
+
 static int page_pool_init(struct page_pool *pool,
 			  const struct page_pool_params *params)
 {
@@ -156,6 +159,8 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
 	/* Track how many pages are held 'in-flight' */
 	pool->pages_state_hold_cnt++;
 
+	trace_page_pool_state_hold(pool, page, pool->pages_state_hold_cnt);
+
 	/* When page just alloc'ed is should/must have refcnt 1. */
 	return page;
 }
@@ -191,7 +196,7 @@ static s32 page_pool_inflight(struct page_pool *pool)
 
 	distance = _distance(hold_cnt, release_cnt);
 
-	/* TODO: Add tracepoint here */
+	trace_page_pool_inflight(pool, distance, hold_cnt, release_cnt);
 	return distance;
 }
 
@@ -222,6 +227,8 @@ static void __page_pool_clean_page(struct page_pool *pool,
 	page->dma_addr = 0;
 skip_dma_unmap:
 	atomic_inc(&pool->pages_state_release_cnt);
+	trace_page_pool_state_release(pool, page,
+			      atomic_read(&pool->pages_state_release_cnt));
 }
 
 /* unmap the page and clean our state */

Re: [PATCH net-next v1 00/11] xdp: page_pool fixes and in-flight accounting

[David Miller]

From: Jesper Dangaard Brouer <brouer@redhat.com>
Date: Thu, 13 Jun 2019 20:28:01 +0200

> This patchset fix page_pool API and users, such that drivers can use it for
> DMA-mapping.
 ...

Please address the minor nits and respin and I'll apply this.

Thanks.